The clasper-siphon sac mechanism inSqualus acanthias and Mustelus canis

Camp. Biochem. Physiol., 1972, Vol. 42A, pp. 97 to 119. Pergamon Press. Printed in Great Britain

THE CLASPER-SIPHON SAC MECHANISM IN SQUALUS ACANTHIAS AND MUSTELUS CANIS

PERRY W. GILBERT1 and GORDON W. HEATH2

‘Mote Marine Laboratory, Sarasota, Florida and Division of Biological Sciences, Cornell University, Ithaca, N.Y.; and *University of Texas, Dental Branch,

Houston, Texas

Abstract-l. Paired ventral, subcutaneous, muscular, epithelium-lined bladders called “siphon sacs” are fdled with sea water in male Squalus acanthias and Mustelus canis by repeatedly flexing each clasper prior to copulation.

2. In mating, one clasper is flexed medially, inserted and is anchored in the oviduct by a complex of cartilages at the clasper tip.

3. Sperm pass from the urogenital papilla into the clasper groove and are washed into the oviduct by sea water and secretions expressed from a siphon sac.

4. Claspers and siphon sacs grow most rapidly when S. acanthias are 48- 58 cm and M. canis are 75-85 cm long; during this period sperm first appear in the testes.

INTRODUCTION

IN ALL sharks fertilization is internal and sperm are introduced into the oviductlof the female by means of male intromittent organs known as “claspers” which are modifications of the caudal portion of each pelvic fin. In spite of the fact that Aristotle (Cresswell translation, 1883), Cuvier & Duvernoy (1846), Smith (1849), Agassiz (1871) and Putnam & Garman (1874) all recognized the claspers of elasmobranchs and commented on their possible function, and Home (1813) discussed a “glandular bag” associated with each clasper, Jungersen (1899) at the close of the last century was compelled to write:

“ . . . I have only been able to advance the understanding of the functions of the ventral appendages very little, most of the questions raised by the different, rather complicated structures, especially in the terminal part, must still be left quite unanswered, as also such facts as the large extent of the glandular bag in most Sharks must still appear mysterious.” The clasper skeleton and its associated musculature has been described super-

ficially by Home (1809, 1810, 1813) and in greater detail by Petri (1877), Jungersen (1899), Goodey (1910), D aniel(1934), Davy (1939) and Matthews (1950) but these latter accounts are either inaccurate or incomplete for the spiny dogfish (Squ&us acanthias). The clasper anatomy of the smooth dogfish (Mustelzcs can&) is mentioned briefly by Leigh-Sharpe (1926), Gilbert & Heath (1955) and Heath (1956). Heath (1960) has prepared the most complete account of clasper anatomy for S. acanthias and M. canis but this has not yet been published.

97

98 PERRY W. GILBERT AND GORDON W. HEATH

Associated with each clasper in sharks is a subcutaneous muscular bladder, the siphon sac or siphon, which ends blindly anteriorly and opens posteriorly into a groove situated along the dorsal surface of the clasper. Petri (1877), Jungersen (1899), Leigh-Sharpe (1920, 1921, 1922, 1924, 1926) and Matthews (1950) have described the gross anatomy of the siphon sacs in some detail and Haack (1903) has studied their microscopic structure in Acanthti and Scyllium. In a primitive shark such as Chlamydoselachus anguineus, each siphon is rudimentary and is little more than an expansion of the proximal end of the clasper groove (Gilbert, 1943). In the ovoviviparous shark, S. acanthias, the siphons are relatively small, and measure but 12 per cent of the total body length (Gilbert, 1958b, 1959). In viviparous sharks however the siphons are much larger and extend forward between the belly skin and somatic musculature on each side of the mid-ventral line almost to the coracoid bar between the two pectoral fins.

Precisely how the claspers and siphon sacs of sharks function has been the subject of much conjecture and accounts of the gross and microscopic structure of these organs have been contradictory. In the present paper the authors propose to clarify for two species of sharks, S. acanthius and M. canis, (1) the mechanics of clasper action and how they are deployed in copulation, (2) the functional role of the siphon sacs and (3) chart the growth of the claspers and siphon sacs for two species of sharks. A detailed description of clasper and siphon sac anatomy will appear elsewhere.

MATERIALS AND METHODS

Twenty-one live and seventy-three preserved spiny dogfish were examined. Sixty-nine live and twenty-six preserved smooth dogfish were also studied. Measurements were made of total body length, clasper length and siphon length of both species. Siphon tissues were preserved in various fixatives for histological and histochemical study. The testes, epigonal organs, pelvic girdle, pelvic fins and claspers were preserved for further examination. In addition several hundred live spiny dogfish, caught in ocean traps off Long Island, New York, were examined for siphon contents. Observations on clasper action were made on spiny dogfish maintained in live cars at the Mt. Desert Island Biological Laboratory, Salsbury Cove, Maine, and on smooth dogfish in large aquaria at the U.S. Bureau of Commercial Fisheries, Woods Hole, Massachusetts. Electrical stimulation of clasper muscles, in living animals, aided in studying their function. For comparative purposes additional dissections were made on several species of carcharhinid sharks from Bahamian waters and the Gulf of Mexico.

THE CLASPERS

Pelvic$n and clasper skeleton

Functionally and anatomically the clasper is part of the pelvic fin and several of the muscles that move the clasper take origin on the cartilages of the fin proper. A brief description of the principal skeletal elements and their related musculature is essential to an understanding of clasper action. The skeleton of the pelvic fin of the male spiny dogfish consists of: basal cartilages, the metapterygium and propterygium, medially; radial cartilages and dermal fin rays or ceratotrichia, laterally; intermediate elements, the joint cartilage and beta cartilage, centrally;

CLASPER-SIPHON SAC MECHANISM IN SQUALUS ACANTHIAS AND MUSTELUS CANIS 99

and the clasper elements, caudally (Fig. 1). The clasper is attached to the metapterygium by means of the short joint cartilage. The clasper proper is made up of the main stem cartilage, to which two marginal cartilages are fused, and four terminal cartilages (Figs. 1 and 2).

-cfL”IC .I”DLE ,. P”OPTEWSI”Y YLT**TLR”OI”Y

*&I. *H*uLc T”.l. uA”**u

” t”D YEWIYTLMIW 2110 DORSAL TLIIYIIIU. c.

” DoRflL X”YI”.L c YE”,“& TEllUlWAL c.

DORSAL VIEW “ENTRALVlEW FIG. 1. Skeleton of entire pelvic fin of S. acunthius; dorsal and ventral aspects.

The metapterygium (basale of Jungersen, 1899) is a substantial basal element which extends caudad from the lateral portion of the pelvic girdle. This cartilage (Fig. 1) is only slightly curved, convexly on the lateral side and concavely on its medial surface, and is more or less uniform in width throughout most of its length. The anterior end narrows to a medial articular projection while the posterior end narrows and curves slightly to articulate with the more distal elements. The short propterygium is also articulated to the pelvic girdle anterior and lateral to the attachment of the metapterygium and is located anterior to the regular radial cartilages.

Most of the rod-like radial cartilages (Fig. 1) extend obliquely laterally and posteriorly from the metapterygium into the thin, flexible portion of the fin. Except for the most anterior and most posterior ray cartilages, each radial consists of two elements, a long proximal segment and a very short, straight, distal segment with a blunt end. Ceratotrichia or dermal fin rays extend on both the dorsal and ventral side distally from the junction of the proximal and distal radials out into the fin. Beyond the distal radials these ceratotrichia, forming the principal portion of the fin, are covered only by a small amount of connective tissue richly supplied by fine blood vessels and by the usual layer of skin.

The clasper proper (Fig. 2) is composed of two intermediate elements known as the joint and beta cartilages, the main stem cartilage to which two marginal cartilages are fused, and four terminal cartilages. The four terminal pieces located distal to the stem cartilage are: the claw (dorsal terminal cartilage), the rhipidion


(secondary dorsal terminal cartilage), the distal basal (ventral terminal cartilage) and the spur (secondary ventral terminal cartilage). Extending caudally from the posterior end of the metapterygium is a short segment, the joint cartilage, which attaches to the stem cartilage distally. The joint cartilage is visible from the ventral side between the metapterygium and stem cartilage, but dorsally it is almost hidden by the beta cartilage. In position the beta cartilage resembles a “knee cap”, being situated over the joint cartilage but also extending cranially onto the posterior end of the metapterygium and caudally onto the stem cartilage. It thus covers the junction between the metapterygium and joint cartilage and between the joint cartilage and the main stem of the clasper. A strong connective tissue capsule surrounding the beta cartilage anchors it to these three cartilages. It also hides a small portion of the proximal end of the last two or three radial cartilages, especially the one or two which are attached to the joint segment. The joint or most flexible articulating point between the fin and clasper is a straight line at the junction of the metapterygium with the joint cartilage and with the beta cartilage.

Continuing caudally from the joint cartilage is the stem cartilage forming the clasper’s principal skeletal piece (Figs. 1 and 2). At its articulation with the joint cartilage, it is round or slightly oval in transection. Progressing posteriorly it becomes more flattened or oval in cross section. Slightly posterior to its articulation with the joint cartilage, a rounded elevation on its medial edge provides an excellent surface for muscular attachment. A dorsal and a ventral marginal cartilage are fused to the stem cartilage. These are often overlooked since they seem to be a part of the stem cartilage. They can easily be recognized, since they are partially calcified and present a different color from the stem cartilage.

Distal to the main stem cartilage, and the two marginal cartilages fused to it, are located four terminal cartilage pieces: the claw or dorsal terminal cartilage and the secondary dorsal terminal cartilage (rhipidion), on the dorsal side; the ventral terminal cartilage and the spur or secondary ventral terminal cartilage on the ventral side (Figs. 1 and 2). A small subsidiary cartilaginous piece, the fifth terminal cartilage, is also located on the ventral side. The stem cartilage narrows and continues caudally for some distance beyond the proximal end of the terminal cartilages. This narrow finger-like end of the stem cartilage known as the end style passes between the ventral terminal cartilage and the claw.

The secondary dorsal terminal cartilage or rhipidion is a thin ear-shaped plate, which, with the claw, forms the dorsal wall of the terminal portion of the clasper groove. A small portion of its proximal edge articulates with the dorsal marginal cartilage. The whole length of its medial edge, except the short portion attached to the dorsal marginal cartilage, is bound to the claw by connective tissue. Its entire convex lateral border is free.

The claw or dorsal terminal cartilage is a hard, partially calcified cartilage, shaped like a question mark, with its distal end curved into a flattened hook which has a cutting edge on its inner margin. Its lateral edge, from the proximal end to the beginning of the hook, is attached to the secondary dorsal terminal cartilage.

FIG. 2. Clasper skeleton of S. acanthias; dorsal aspect.

FIG. 4. Claspers of S. acanthius in resting position; ventral aspect.

nulated. FIG. The

5. Right clasper of S. acanthius flexed medially when electrically distal ele :ments (basal, rhipidion, claw and spur) are also flexed,

tb e condition after insertion in the female; ventral aspect.

stin sin


The proximal third of its medial edge is attached to the end style of the stem cartilage. The middle third of its medial edge is attached to the ventral terminal cartilage. The distal third, representing the hooked portion of the claw, is free of attachments to other skeletal parts and the skin. In the resting position the point of the hook is directed laterally. Upon flexion, the claw is rotated on its own axis 180” so that the hook points medially.

The ventral terminal cartilage or distal basal is a long, broad, flattened cartilage with its edges curved upward to form a shallow trough that marks the distal end of the clasper groove. At its proximal end the ventral terminal cartilage articulates medially by its shorter head with the ventral marginal cartilage. Its longer lateral head is attached by tough connective tissue to the head of the spur. Part of the tendon of the outer lip muscle inserts on the dorso-lateral edge of the ventral terminal cartilage and encloses a small subsidiary cartilage.

The spur or secondary ventral terminal cartilage is long, slender, partially calcified and curves gently outward to terminate in a sharp point. The distal two- thirds of the spur is free of skin and without attachments to other parts. The proximal end of the spur has a rounded head which projects medially to articulate, and attach by strong ligaments, with the long head of the ventral terminal cartilage. A part of the tendon of the outer lip muscle inserts on the head of the spur as well as on the ventral terminal cartilage. In the resting position the spur is retracted and lies against the lateral edge of the ventral terminal cartilage.

Clasper action

When spiny dogfish mate the male flexes one clasper medially before inserting it into the cloaca and oviduct of the female. After insertion of the clasper, the terminal pieces are then flexed, thus anchoring the clasper firmly within the distal end of the oviduct. Flexion of the whole clasper and flexion of the terminal cartilages are therefore independent of each other.

The flexor muscle (Fig. 3) is responsible for antero-flexion of the clasper. The clasper is bent at the “knee” joint and first pulled medially. As contraction is continued the distal end of the clasper crosses the midline and is bent forward 90-100” from its original position (Figs. 4 and 5). The dorsal, middle and ventral divisions of the flexor muscle working together insure the clasper of being bent forward without being rotated. Thus the dorsal side with its open clasper groove remains dorsally. It is important that the clasper be flexed medially and forward rather than ventrally and forward, for in the latter case the original dorsal surface, bearing the clasper groove, would face ventrally and away from the urogenital papilla. The short fibers of the middle division of the flexor muscle passing over the “knee” seem best suited for the initial medial bending of the clasper. After the clasper has been flexed part of the distance, the long fibers of the dorsal and ventral divisions which insert more distally draw the clasper forward to the full extent of its flexed position. When the dorsal and ventral divisions are cut, electrical stimulation of the middle division will flex the clasper less than half the full extent


it moves when all three divisions are intact. The initial movements by the middle division are probably aided by action of the adductor muscle.

The terminal cartilages of the clasper are flexed or elevated by contraction of the dilatator muscle (Fig. 6). When the dilatator muscle relaxes these terminal elements return to the resting position by the stretched elastic tissue surrounding them and by the contraction of the outer lip muscle which inserts on the head of the spur and distal basal (Fig. 7).

FIG. 3. Pelvic fin and clasper musculature of S. acanthias; dorsal aspect.

The dilatator muscle is quite simple in itself, but its contraction results in movement of all the terminal cartilages. This includes rotation of the claw through 180” and movement of the other three terminal pieces in different directions (Fig. 6). This remarkable action, noted by Petri (1877) and Jungersen (1899), depends not so much on unusual features of the muscle as on the special structure and interaction of the skeletal parts. The cartilages have opposing projections, special attachments, a sliding tract, levers and fulcrums, and unusual shapes which permit a single muscle to perform the action which would otherwise require several muscles. The principal insertion of the broad dilatator tendon or aponeurosis is on the ventral and medial borders of the ventral terminal cartilage. Contraction of the dilatator muscle moves this cartilage obliquely medially and slightly ventrally. Attachment of the middle third of the claw to this cartilage also moves the claw medially. This movement of the claw would be a simple operation were it not also connected to other parts. It is rotated 180” on its long axis by the following process. Part of the broad dilatator tendon is inserted on the dorso-lateral edge of the


proximal third of the claw which tends to draw the claw medially while the ventral terminal cartilage tends to draw it medially and ventrally. The projection of the end style between the ventral terminal cartilage and the proximal third of the claw tends to hamper movement of the claw. Since the pull on the claw by the ventral terminal cartilage and by the dilatator tendon is great enough to overcome the end style blockage, the claw is rolled around the dorsal surface of the end style for its attachment to the end style is more fixed than the moveable lateral edge. Since the secondary terminal cartilage is attached to the claw, it is also drawn medially and dorsally with the claw. The free lateral edge of the secondary dorsal terminal cartilage is thus widely separated from the ventral terminal cartilage.

FIG. 6. Clasper mechanism in S. acanthias. After insertion of a clasper into the female the dilatator muscle (d.m.) contracts causing the ventral terminal cartilage (v.t.c.) and dorsal terminal cartilage or rhipidion (r.) to flex at right angles to the stem cartilage (s.c.). Simultaneously the claw (c.) revolves on its long axis through 180” and the spur (s.) moves outward. Claw and spur each penetrate the wall of the oviduct thus securely anchoring the clasper. c., claw; d.m., dilatator muscle; o.l.m., outer lip muscle; r., rhipidion; s., spur; s.c., stem cartilage; v.t.c., ventral

terminal cartilage.

Movement of the ventral terminal cartilage brings about a lateral projection of the spur in the following manner. When the ventral terminal cartilage moves medially its short median head is held against the ventral marginal cartilage to which it is bound by a stout ligament. This causes a lateral and posterior projection of the long lateral head which is bound by a tendon to the head of the spur. The neck of the spur works against the lateral projection of the ventral marginal


cartilage while the head is prevented from moving medially by the inner median projection of the ventral marginal cartilage. Since the head of the spur is tightly bound to the lateral head of the ventral terminal cartilage and thus must move caudally with that cartilage, it glides against the median projection of the ventral marginal cartilage. As the curved neck is bound to the lateral projection of the ventral marginal cartilage, it works against that projection like a lever against a fulcrum. Thus when the head of the spur glides caudally, its free distal end swings outward away from the other terminal pieces of the clasper.

d.m.

FIG. 7. Clasper mechanism in S. acunthkzas. Before withdrawal of the clasper the dilatator muscle (d.m.) relaxes and the outer lip muscle (o.1.m.) contracts returning all four distal elements (ventral terminal cartilage, rhipidion, claw and spur) to

their resting position. d.m., dilatator muscle; o.l.m., outer lip muscle.

When the terminal cartilages have thus been moved from their resting position by action of the dilatator muscle, the elements are separated in three directions forming three edges of a pyramid. The ventral terminal cartilage has moved medially and ventrally, the claw and secondary dorsal terminal cartilage medially and dorsally and the spur laterally. In this position these cartilages are said to be erected or flexed.

The outer lip muscle is the only extensor muscle found in the clasper. It inserts by a stout tendon to the head of the spur and, via the tendon which encloses the subsidiary ventral terminal cartilage, to the dorso-lateral ridge of the ventral

CLASPER-SIPHON SAC MECHANISM IN SQUALUS ACANTHIAS AND MUSTELCJS CANIS 105

terminal cartilage. Relaxation of the dilatator muscle and contraction of the outer lip muscle causes the ventral terminal cartilage and the head of the spur to be pulled cranially back to the resting position. Now the curved neck of the spur acts against the lateral projection of the ventral marginal cartilage causing the free distal end of the spur to swing medially to its resting position. The head of the spur moves back into place by gliding in the slot between the inner median dorsal and outer lateral projections of the ventral marginal cartilage. Retraction or return to the resting position of the terminal cartilages, including the spur and ventral terminal cartilage, after the dilatator ceases to exert its action is probably due primarily to elasticity of tissue surrounding these parts. This view is expressed by Petri (1877), Jungersen (1899) and Matthews (1950). The elastic ligaments attaching these cartilages are stretched when the elements are flexed. That these cartilages will return to the resting position when all muscles are removed was confirmed on living animals. The action of the outer lip muscle on the spur and ventral terminal cartilage gives added force to their retraction,

MATING POSITION IN SHARKS

Bigelow & Schroeder (1948, 1953) have repeatedly pointed out the paucity of published information concerning the mating behavior of elasmobranch fishes. To the best of our knowledge only two photographs and two line drawings have ever been published that illustrate sharks in the act of mating. The first illustration is that of Bolau (1881) (Fig. 8), a 1 ine drawing of paired Scyliorhinus canicula. A

FIG. 8. Sketch of male and female S. canicula in mating position. Redrawn from Bolau.

fine photograph of S. canicula mating was taken by Schensky at the Helgoland Aquarium and was first published in 1914. Subsequently Dr. Douglas Wilson photographed a pair of S. canicuka in copulo and his photograph appears as Plate XV in a book by Hardy (1959). In all illustrations the male is shown coiled about the pelvic region of the female and in this position it is obvious that but one clasper,


which has been flexed medially, could be inserted into the cloaca and oviduct. Although neither Squalus nor Mustelus have ever been observed during copulation, it is probable that their mating position is similar to that of Scyliorhinus (Gilbert, 1958a).

The only species of shark, other than S. canicula that has been figured in the act of mating is Heterodontus francisci in a paper by Dempster & Herald (1961). They state, “The pair were average in size and the male, measuring 274 inches, had seized a 284 inch female by the left pectoral fin and was firmly holding on to it with his mouth. The female was lying partially on her left side facing the male and did not appear to be making any great effort to get away from him. In a short time he had manipulated his body so that his tail occupied a position over her back immediately in front of the second dorsal fin. By using her second dorsal spine as an anchor and, at the same time, holding on to the left pectoral fin with his mouth-the mid-region of his body being in a position to move freely-he was able to thrust his right clasper into her vent. The left clasper played no part whatsoever in the sexual act; it hung loosely in the water.”

It is entirely possible that the mating position described here for smaller species of sharks such as Scyliorhinus and Heterodontus is not the same for larger species with less flexible bodies.

THE SIPHON SACS

The siphon sacs of male sharks are paired, subcutaneous, muscular, epithelium- lined bladders, situated in the pelvic region on each side of the midline between the skin and belly musculature. Each sac ends blindly anteriorly and opens into the clasper groove posteriorly. In S. acanthias (Fig. 9) they are relatively small, measuring ca. 12 per cent of the total body length and each is capable of holding a maximum of 6-15 ml of fluid. When the muscular walls of the sac are stimulated electrically they contract to 85 per cent of their original length. The wall of the spiny dogfish siphon is composed of four well-defined layers of tissue: an outer layer of loose connective tissue, a layer of striated muscle, a middle layer of loose connective tissue containing a large number of blood vessels and nerve fibers, and an epithelial layer bordering the lumen of the sac. This epithelium consists primarily of a basal layer of cuboidal or polygonal cells, a middle layer of tall cells and an outer layer of smaller polygonal cells. Most of the tall cells forming the middle layer are filled with secretion. These goblet cells are of the merocrine type. The fact that neither mitotic figures nor pycnotic nuclei are seen suggests that the goblet cells are not replaced after discharging their secretion. Tissues of spiny dogfish siphon sacs collected during the period from 13 June to 30 November revealed no histological changes during that time. The siphon sacs normally contain a small quantity (0.2 ml) f 1 o c ear, sticky fluid which is secreted by the numerous large goblet-like cells present in the stratified epithelium lining the lumen of the sac. The secretion has a pH of 5.8, and contains urea (56188 mM), Na+ (204-362 mN), Cl- (265-403 mN), K+ (5.8 mN) and 4.42 mg N/ml. Paper chromatograms fail to detect glucose, fructose or sucrose in the secretion. Mann


(1960) found the adult spiny dogfish clasper siphon to be a rich source of serotonin, “the concentration of which exceeds by many times the values recorded for other animal organs . . . . The presence of so much serotonin in a secretion which represents an integral part of semen suggests that, in the spiny dogfish in any event, serotonin may play a part in the reproductive process, either by affecting the mechanism of copulation and ejaculation in the male, or by eliciting contractions of the female reproductive tract, thus influencing passage of sperm and fertilization”

SPINY DOGFISH

FIG. 9. S. acanthias, showing extent of siphon sacs (broken line) situated between belly skin and body musculature; ventral aspect.

The siphon sacs of the smooth dogfish, M. canis, are much larger than those of S. acanthias and measure 30 per cent of the total body length (Fig. 10). They extend anteriorly between the belly skin and body musculature almost to the coracoid bar with which the pectoral fins articulate. The wall of the smooth dogfish siphon sac is very similar in cellular arrangement to that of the spiny dogfish, except that all tissue layers in the smooth dogfish are much thinner. The greatest difference between the two species is seen in the lining epithelium. The epithelium is composed of stratified polygonal cells all more-or-less alike until the secretory droplets accumulate in a cell in quantities great enough to distort it into a rounded goblet cell. These goblet cells are quite scattered compared to the thickly popu- lated goblet cells of the spiny dogfish siphon. The goblet cells are classed as


merocrine, the cytoplasm being replaced after discharge of the secretory product. Neither mitotic figures nor pycnotic nuclei are seen in the epithelial cells. Tissues of the siphons of smooth dogfish taken during the period from 9 June to 31 August show no histological differences.

SMOOTH DOGFISH

FIG. 10. M. cmis, showing extent of siphon sacs (broken line) situated between belly skin and body musculature; ventral aspect.

MECHANISM FOR FILLING THE CLASPER SIPHONS

While one of us (P. W. G.) was working during July-August at the Mt. Desert Island Biological Laboratory, there were many opportunities to observe mature male spiny dogfish swimming about in a live car at the dockside. On one occasion I noticed a mature male repeatedly flexing its right clasper medially and when I netted this animal I noted that the right siphon was swollen and its full outline could be seen beneath the belly skin. When I pressed this siphon, approximately 5 ml of sea water emerged into the clasper groove. After placing this shark back in the live car, I found it possible to pump water into the siphon by manually moving the clasper back and forth, from right to left, through an arc of 90-120” in the plane of the shark’s body, thus simulating the movement we had previously obtained when the clasper muscles of a live dogfish were electrically stimulated. I noted that when the clasper was flexed medially a lip projected ventrally at the proximal end of the clasper groove. This lip was on the outer margin of the clasper groove and when the clasper was flexed medially the lip served to shunt


sea water into the groove, through the apopyle and thence into the siphon. By repeatedly flexing the clasper it was therefore possible to pump as much as 10 ml of sea water into the siphon of that side. When the other clasper was flexed it was possible to fill the other siphon with sea water. Thus, for the first time, it became clear how a live shark might fill its siphons with sea water. Expulsion of the water could be readily accomplished by the contraction of the compressor muscle that forms a significant component of the siphon sac wall.

One clasper was then tied in the flexed condition on an anesthetized shark and this shark was towed through the water, In doing so, the lip which projected ventrally, on the now caudal margin, at the base of the clasper groove directed sea water through the apopyle and into the siphon. It would therefore be possible for a dogfish to swim leisurely through the water with one clasper flexed medially and thus fill the siphon of that side.

We believe it is therefore possible for a shark to fill its two siphons with sea water either by repeatedly flexing its right and left clasper thus pumping sea water into the siphons, or by swimming through the water with first one clasper and then the other flexed medially for a few minutes thus directing water upward into the clasper groove, through the apopyle, and into the siphon. Leigh-Sharpe was therefore correct when he surmised that the siphons served as sea water reservoirs and contracted during copulation to wash sperm along the clasper groove into the oviduct. He was incorrect however in stating that the siphons are normally filled with sea water. In addition to those utilized in this study, we have examined many hundred, live, freshly caught spiny dogfish and, with the exception of the case cited above at the Mt. Desert Island Biological Laboratory, the siphons have al- ways been empty. Moreover Leigh-Sharpe failed to explain how sea water is introduced into an empty siphon situated between the belly skin and body musculature.

GROWTH OF CLASPERS AND SIPHON SACS

The following measurements were taken for both species. Total length of the animal was taken as the distance from the tip of the snout to the end of the vertebral column in the caudal fin. By holding this fin so that light passes through it, the end point of the vertebral column can be seen easily and marked with a soft lead pencil. Another measurement commonly used is from tip of snout to tip of caudal fin (Home, 1809; Templeman, 1944). Goodey (1910), Ford (1921), Hickling (1930) and Von Bonde (1945) give body length measurements but do not state how they were determined. Other workers have measured distance from tip of snout to center of caudal emargination (Matthews, 1950; Matthews & Parker, 1951). Leigh-Sharpe (1921), at least in some of his specimens, measured distance from snout to posterior end of claspers because the tails were removed before the animals were shipped to him. Most workers, if they give body length measurements at all, do not state how they were determined.

Measurements of paired structures were made on the left side of the animal and sections of the siphon sac for microscopic examination were taken from the

110 PERRYW. GILBERT AND GORDON W. HEATH

left side. The length of the pelvic fin was taken as the distance from the midline of the anterior border of the pelvic girdle to the most posterior tip of the fin. Two measurements were made for the clasper. The first was from the junction of the metapterygium with the clasper cartilages to the tip of the clasper; that is, it included all elements distal to the metapterygium. A second measurement was taken from the mid-line of the anterior border of the pelvic girdle to the posterior tip of the clasper. This would of course include part of the pelvic girdle and fin, as well as the clasper itself. The length of the siphon sac was measured from the anterior tip of the apopyle to the anterior tip of the sac, the apopyle being the slit-like opening of the siphon sac into the clasper groove. It should be noted that the lateral portion of the adult siphon extends slightly caudal to the anterior tip of the apopyle, but measurement of this posterior part of the sac is difficult to determine in young specimens where the sac fades into the clasper groove.

Since the claspers and siphon sacs are secondary sexual organs, it is not sur- prising to find they have a rapid growth period at about the time sexual maturity is reached. Our data, summarized in the growth curves (Figs. 11 and 12), reveal

100 1

90

I Gmwth ot Cbrpr(dothd ih) OId cidmn MC (cotldlk)ln the

0 IO 20 30 40 SO 60 70 60

STANIMRD LENGTH IN Cm

FIG. 11. Growth curve of clasper (broken line) and siphon sac (solid line) in spiny dogfish, S. acanthias.

a slow increase in length for both the claspers and siphon sacs in the immature sharks of both species. This is followed by a period of very rapid growth for these structures when their rate of increase is much greater than general body growth or growth of a non-sexual character such as the pelvic fin. Following this rapid growth period the claspers and siphon sacs continue to grow but at a much slower rate.

CLASPER-SIPHON SAC MECHANISM IN SQUALUSACANTHIAS AND MUSTELCJSCANIS 111

In spiny dogfish claspers and siphons grow most rapidly when its body length increases from 48 to 58 cm. Claspers and siphons of smooth dogfish grow most rapidly when the body length increases from 75 to 85 cm. It is during this period of rapid clasper and siphon growth that spermatozoa first appear in the testis of both species.

400-

360-

360- Gmwth ofcbopr(dottrd Iii)md

340- siphon sot (solid I~u)in ths SMOOTH DOGFISH

320- BB

300-

260-

:260-

2240-

x220-

t 200-

!? ISO-

160-

ISO-

120.

IOO-

60-

60-

40-

20- __-- 0 ” ” ” ” ” ’ “1 t

lO2030406060706060lGOI0120l3Ot4O40

STANMRD LENGTH IN Cm

FIG. 12. Growth curve of clasper (broken line) and siphon sac (solid line) in smooth dogfish, M. canis.

DISCUSSION

Although Aristotle recognized that the “ventral appendages” of male sharks differed from those of the female, Home (1809, 1810, 1813) was the first to refer to them as “holders” or “claspers”. He reports that these structures “have been mistaken for penises by many physiologists” but have been more rightly considered by others as claspers to hold the female. Home (1810) presents a drawing showing S. acanthkzs with “the holders in their extended state, as they appear when the male is clasping the female. In this state of the parts the penis is brought forward, and projects externally.” He regards the urogenital papilla as the penis when he records, “The insertion of the penis into the female is not unlike that of the common fowl, but the penis is fitted to inject the semen further into the oviduct

112 PERRY W. GILBERT AND GORDONW.HEATH

than can be done by a grooved penis of the cock.” His drawing of the “clasping” position of the claspers was surely constructed from supposition since it is impossible for the claspers to move ventrally and forward in the manner Home suggests.

Agassiz (1871), among others, dismisses the concept of Home and states that the two claspers are rotated inward and forward, bringing the furrows on their inner surface into parallel contact. “Being then introduced into the body of the female, their extremities diverge in the two oviducts, and the glans being un- covered exposes a sharp cutting instrument, which would injure the organs of the female if she resisted . . . . What was formerly supposed to be the penis [urogenital papilla] is too small, and of insufficient length to accomplish fecun- dation. The penis consists of the two long flexible finger-like fins, furnished with two projectile spinous appendages . . . .”

Putnam & Garman (1874) state that while the so-called claspers of sharks and skates had been generally regarded as having something to do with copulation, very little direct information had been published on the subject to that time. According to them, “It was, however, from the researches of Agassiz, made in 1856-7 but not published, that the knowledge that the ‘claspers’ were true copulatory organs became generally known. Agassiz afterwards made further observations, and proved that these appendages to the ventral fins were capable of erection.” Putnam & Garman contend “the claspers are not only true intromittent organs, but the cutting edges and sharp points of the distal end serve to open the closed oviducts of the virgin sharks in order to allow impregnation to take place.”

Bolau, working at the Zoological Gardens of Hamburg, was the first to actually observe and describe the mating activity of sharks. He observed mating in S. canicula on two occasions and a woodcut was prepared from a pair of sketches he drew. Figure 8 is a drawing based on this original print. Bolau (1881) gives a description of the manner in which the male was entwined about the female. The important point made is that only one clasper was inserted into the genital opening of the female at each mating. In the first mating observed in February 1878, he did not notice which clasper was inserted; but in a mating that took place in March 1879, the right clasper was inserted. In each of these two cases coitus lasted about 20 min. Bolau notes that prior to insertion, the rough surface of the clasper is made greasy and slippery by the secretion of the siphon sac. According to his belief, when the clasper is completely inserted within the cloaca of the female, the cloaca1 openings of both animals lie directly against each other and the outflow of seminal fluid can pass directly into the female’s cloaca which has been widened by the clasper. He is unable to say whether the “canal on the inner side” of the clasper is functional or not.

Jungersen (1899) devotes most of his paper to describing the skeleton and muscles of the clasper, mentioning the siphon sacs only incidentally. Concerning the claspers, he writes, “of their functions only little is known with certainty, and on this point I am not able to bring new facts of any importance.” He reports the first reliable recorded observation of copulation is that by Bolau (1881).

CLASPER-SIPHON SAC MECHANISM IN SQUALCJS ACANTHIAS AND MLJSTELUS CANIS 113

Jungersen regards this observation as very important since it establishes that the clasper is really introduced into the genitals of the female. He regrets, however, “it decides nothing with regard to the most important question, whether the appendix really conveys the semen or not. As to this question we are still reduced to draw our inferences from the structure of the organ.” On this basis he feels the clasper groove cannot be the duct for the semen. He believes it impossible for the sperm to get into the clasper groove because of its location. Also he feels the claspers are not able to move in such a way as to have the groove approach the cloaca. Jungersen obviously did not understand there are muscles capable of flexing the claspers medially and forward, even though he mentions Agassiz’s paper explaining this movement. He argues the claspers would have to be turned 180” on the longitudinal axis in order to form the tube mentioned by Agassiz. Thus, he misinterprets Agassiz to mean the lateral edge of the clasper is rotated medially on its longitudinal axis rather than being bent medially and forward. He also points to the observations of Bolau that only one clasper is inserted at a time; however, he admits this may not be the case in all other selachians. He is of the opinion that the semi-tubular form of the appendix cannot directly have anything to do with the transfer of semen and that its most immediate purpose is the trans- portation of the gland secretion.

Jungersen then gives his own opinion as to the function of the claspers. First he believes the organ is designed to be introduced into a cavity such as the oviduct and that it is able to fix itself in this cavity by dilation of the terminal parts. Bolau has shown the first part to actually happen. Jungersen believes the claspers perform other functions as well. Among these are the functions of awakening sensu- ality and opening or widening the mouths of the oviducts in virginal females. He continues, “though I cannot imagine that the appendix-slit should form a duct for the sperm, I still think it probable that the appendages in some way or other subserve the conveying of the semen, so that it is not conveyed by means of the urogenital papilla of the male alone and I also suppose that the secretion of the glandular bag subserves this object.” He says the glandular secretion is emptied not only through the terminal end of the clasper but also at the base. This would not only lubricate the clasper but the whole immediate area surrounding the cloaca of both the copulating animals. Jungersen admits that he knows little about the siphon sac secretion but objects to Agassiz’s opinion that the function of the sac is the storage of sperm. He cannot see how the bag could be filled and, more important, spermatozoa have not been found there although its contents have been subjected to microscopical examination.

Initiation of the present investigation, and especially that portion dealing with the siphon sac, was greatly influenced by the theory of Leigh-Sharpe (1920) stating the siphons are filled with sea water. After examining the siphons of “some hundreds” of S. canicuh in which he found nothing more than slight traces of “what looked like mucus” in some of them, Leigh-Sharpe states, “At the same time the walls of the siphon are so very muscular as to suggest the injection and expulsion of fluid of some sort, so I was reduced to considering whether or not


that fluid might be merely sea water.” Leigh-Sharpe sought to test this theory as follows. He injected powdered carmine suspension into the siphon and bent the clasper sharply forward. He then pressed upon the distended siphon with a finger, “simulating in this the natural muscular contraction of the living animal.” [underscoring ours]. From this last statement, we assume the animals used in his experiments were dead. He reports the carmine he injected spurted voluminously from the distal end of the clasper groove to a distance of 3 or 4 ft. Although Leigh-Sharpe declares that nothing is ever found in the siphon except occasionally a small amount of mucus-like fluid, he subsequently states, “It must be remembered that in life the siphon does not require to be filled as in the preceding experiment, since it normally contains sea water.”

Concerning the function of the claspers Leigh-Sharpe (1921) reports that a pair of sharks, Galeus vulgaris, kept in tanks for a few days were killed while copulating. He states that both claspers were inserted when examined. He relates earlier that all the animals captured had been injured and were kept alive only a few days. A helper killed the copulating animals; they were not observed by Leigh-Sharpe himself. Whether the circumstances leading to this record of both claspers being inserted at the same time is a reliable observation and, if so, whether it represents the usual situation is debatable.

Matthews (1950) takes issue with Leigh-Sharpe that the siphons are normally filled with sea water. He states the siphons are normally empty and collapsed with their internal and external walls in contact and finds it difficult to understand how the siphons could be filled with sea water since there appears to be no muscular arrangement by which this might be accomplished. Matthews says little has been added to our knowledge of the pairing of elasmobranchs since Bolau (1881) made his observations on the copulation of cat sharks and showed in a drawing that the male entwined his body around that of the female. Matthews believes it probable that similar contortions accompany pairing in other elasmobranchs, but it is less likely that much entwining occurs with the rather rigid body of large sharks such as the basking shark, Cetorhinus. Matthews never actually observed mating of sharks but said, “It can however, be definitely stated that in Cetorhinus one clasper only is inserted at a time into the vagina [cloaca] of the female.” As evidence of this he relates the pattern of lacerations on the pad-like lateral walls of the cloaca showing they could have been made only by one clasper being inserted at a time. He interprets these lacerations to have been produced by the claw of the clasper of the male during copulation. He points out that the only direct evidence of the number of claspers inserted at mating is that of Bolau (1881) who observed the number is one. He states the photograph published by Schensky (1914) shows no details as to the number of claspers inserted at a time.

Of the theories concerning siphon and clasper function reviewed above some, for lack of evidence, have no merit; others are plausible as far as they go. Agassiz’s theory of sperm storage in the siphon sacs seems to be without supporting evidence and is no longer seriously considered. No reliable reports of finding sperm in the siphon sacs have been made. Jungersen, Leigh-Sharpe and others who have

CLASPER-SIPHON SAC MECHANISM IN SQUALUS ACANTHIAS AND MCJSTELUS CANIS 115

examined the siphons of hundreds of sharks have never found spermatozoa in them. In our study siphon sacs from a large number of both spiny dogfish and smooth dogfish were examined microscopically and spermatozoa were never found in any of the siphons. We believe that Leigh-Sharpe has correctly surmised that the siphons function in storing sea water that is utilized in washing sperm along the clasper groove into the oviduct. However, he presents no convincing proof that this is so, nor does he give any explanation as to how sea water gets into the siphons in the first place. Leigh-Sharpe’s statement that the siphons are normally filled with sea water has no basis in fact and he himself admits he has never found sea water in the siphon of any freshly caught shark. In this paper we do propose a method by which sea water is pumped or funneled into a siphon by clasper flexion, and provide experimental proof that this is possible. In addition we have noted, in our histological studies, that the lining epithelium of the siphon sacs is richly endowed with secretory cells which produce a viscous, mucous-like substance that would be of value in lubricating the clasper. Moreover Mann (1960) has found the siphon secretion of S. acanthias to be a very rich source of serotonin (5-hydroxytryptamine) which is known to stimulate uterine contractions. Mann reasons that it may produce contractions of the female reproductive tract and thus facilitate sperm passage and fertilization.

Convincing arguments of various investigators have been reviewed against considering the “claspers” as having a prehensile function, at least in the sense of holding the female between the two claspers. They are not suited anatomically for this purpose. There are no muscles capable of directing the claspers around the body of the female, and electrical stimulation does not show such a movement to be possible.

The direct evidence reported by Bolau (1881) that only one clasper is inserted at a time is supported by the indirect evidence offered by Matthews (1950). The one report by Leigh-Sharpe (1922) that two claspers are inserted at the same time is questionable, but if true, may not represent the usual case. It would appear impossible for both claspers of either the spiny dogfish or smooth dogfish to be inserted together for, in their flexed condition, their distal ends are too widely separated (Fig. 5).

It has been suggested that the clasper, once inserted, serves to dilate the oviduct or uterus and thus permit sperm to be transferred by the urogenital papilla either directly as a kind of penis or indirectly through the water and siphon secretion in the vicinity of the two cloacas. It seems logical that the passage of sperm into the oviducts would be hindered by having that tube plugged with a structure as large as the clasper. We cannot see how this situation can aid the passage of sperm into the oviduct.

In the light of all the evidence the most logical function for the clasper is that of conveying sperm into the oviduct. Leigh-Sharpe and Matthews have both shown that sperm are able to pass into the clasper groove. This can also easily be demon- strated with the two species we have studied. In fact many of the animals examined, especially the smooth dogfish, had their clasper grooves filled with sperm. Contrac-


tion of the siphon sac, by the compressor muscle, forces its secretion and sea water out through the clasper groove and into the oviduct, carrying the sperm. There is little doubt that some of this secretion flows over the clasper surface to lubricate it prior to insertion. After the clasper is inserted, the distal elements afford excellent anchorage. In addition to lubricating the clasper and serving, along with sea water, as a transfer medium for the sperm, the siphon sac secretion may possibly have an activating action on the sperm and stimulate contractions of the oviduct, thus facilitating sperm passage and fertilization.

SUMMARY

1. The posterior portion of each pelvic fin of male sharks is characteristically modified into an elongated intromittent organ known as a clasper.

2. The clasper of S. acunthti is composed of the main stem cartilage, with which two marginal cartilages are fused, and four terminal cartilages located distal to the stem cartilage. The terminal cartilages include: the claw (dorsal terminal cartilage), the rhipidion (secondary dorsal terminal cartilage), the distal basal (ventral terminal cartilage) and the spur (secondary ventral terminal cartilage).

3. Electrical stimulation of clasper muscles of S. wunthius and M. canis reveals that, during copulation the clasper is flexed medially, forming an angle of ca. 90” with the long axis of the body. One infers therefore that the copulatory position is similar to that in S. canida in which species the male coils about the cloaca1 region of the female and inserts but one clasper at a time.

4. Once the clasper of S. acanthias is inserted into the oviduct, its distal end bends sharply and causes the prominent spur to project outward in the opposite direction. Simultaneously the claw, the flat surface of which had previously rested against the rhipidion and distal basal, now revolves through 180” and, together with the spur, penetrates the wall of the oviduct thus securely anchoring the clasper.

5. Associated with each clasper in sharks is a subcutaneous muscular, epithelium-lined bladder, the siphon sac or siphon, situated on each side of the midline between the skin and belly musculature. Each sac ends blindly anteriorly and opens into the clasper groove posteriorly through the apopyle. Claspers and siphons grow most rapidly when S. acanthias are 48-58 cm and M. canis are 75- 85 cm in total length; during this period sperm first appear in the testes.

6. In S. acunthius the sacs are relatively small, measuring ca. 12 per cent of total body length. In M. canis the sacs extend forward almost to the coracoid bar and measure cu. 30 per cent of total body length.

7. The siphon sacs of S. acanthias normally contain a small quantity (O-2 ml) of clear, sticky fluid which is secreted by numerous large goblet-like cells present in the stratified epithelium lining the lumen of the sac. The secretion has a pH of 5.8, and contains urea (56-188 mM), Na+ (204-362 mN), Cl- (265403 mN), K+ (5.8 mN) and 4.42 mg N/ml.

8. Prior to mating S. acanthius and M. canis may pump sea water into each siphon by repeatedly flexing the claspers. Sea water may also enter a siphon when

CLASPER-SIPHON SAC MECHANISM IN SQCJALUS ACANTHIAS AND MUSTELUS CANIS 117

the clasper of that side is held in the flexed condition while the shark swims

through the water. 9. Sea water is expressed from the siphon lumen when the compressor muscle

of the siphon contracts. During copulation sperm that have passed from the urogenital papilla into the clasper groove are thus washed along the groove into the oviduct by sea water from the siphon.

10. There is no evidence that the siphons serve as reservoirs for the storage of sperm in any species of shark we have examined.

AcRnowle&errrents-This work was carried out at Cornell University, Ithaca, New York; the Mount Desert Island Biological Laboratory, Salsbury Cove, Maine; the Marine Bio- logical Laboratory, Woods Hole, Massachusetts; the Lemer Marine Laboratory, Bimini, Bahamas; and the Mote Marine Laboratory, Sarasota, Florida. For the facilities at each of these institutions the authors are most grateful. Portions of this study were supported by a grant to the Mote Marine Laboratory from the National Science Foundation for support of the R/V Rhincodon and from a contract between the Office of Naval Research and Cornell University. Dr. William A. Wimsatt gave valuable histological assistance and Dr. Bodil Schmidt-Nielsen and Dr. David W. Bishop kindly provided analyses of the siphon sac fluid.

REFERENCES

AGASSIZ L. (1871) On the method of copulation among Selachians. PYOC. Boston Sot. nut. Hist. 14, 339-341.

ARISTOTLE (1883) History of Animals. (English Translation by R. C-WELL.) P. Bell, London.

BICELOW H. B. & SCHROEDER W. C. (1948) Fishes of the Western North Atlantic. In Sharks, Pt. 1, Chapt. 3. Mem. Sears Fdn mar. Res. 1 (l), 59-546.

BICELOW H. B. & SCHROEDER W. C. (1953) Fishes of the Gulf of Maine. Fishery Bull. Fish Wildl. Serv. U.S. 53, l-577.

BOLAU H. (1881) Uber die Paarung und Fortpflanzung der Scyllium-Arten. Z. wiss. Zool. 35, 321-325.

CUVIER G. & DUVERNOY G. L. (1846) Lecons d’Anatomie comparee, Tome 8. Paris. DANIEL J. F. (1934) The Elasmobrunch Fishes. The University of California Press, Berkeley,

California. DAVY J. (1839) On the male organs of some of the cartilaginous fishes. Phil. Trans. R. Sot.

Lond. Part I 129, 139-149. DEMPSTER R. P. & HERALD E. S. (1961) Notes on the hornshark, Heterodontusfrancisci, with

observations on mating activities. Oct. Paaers Cal. Acad. Sci. 33, l-7. FORD E. (1921) A contribution to our knowledge of the life-histories of the dogfishes landed

at Plymouth. g. Mr. biol. Ass. U.K. (New Series) 12, 468-505. GILBERT P. W. (1943) The morphology of the male urogenital system of the frilled shark,

Chlamydoselachus anguineus. J. Morph. 73, 507-528. GILBERT P. W. (1958a) Clasper action and probable mating position in the spiny dogfish,

Squalus acanthius. Anat. Rec. 130, 411. GILBERT P. W. (1958b) The siphon sacs and their secretion in the spiny dogfish, Squalus

acanthias. Anat. Rec. 130, 411. GILBERT P. W. (1959) Claspers and siphon sacs of the spiny dogfish, Squalus acunthias.

Bull. Mt Desert Isl. biol. Lab. 1959, 46-47.


GILBERT P. W. & HEATH G. W. (1955) The functional anatomy of the claspers and siphon sacs in the spiny dogfish (Squalus acanthias) and smooth dogfish (Mustelus canis). Anat. Rec. 121, 433.

GOODEY T. (1910) A contribution to the skeletal anatomy of the frilled shark, Chlumydosel- achus anguineus Gar. Proc. zool. Sot. Lond. Pt. 1, 540-571.

GUDGER E. W. (1915) The gland of the clasper in sharks. Science, N.Y. 41, 436-437. HAACK W. (1903) Uber Mundhiihlendriisen bei Petromyzonten. Zeit. fiir wiss. 2001. 75,

112-146. HARDY A. (1959) The open sea: its natural history. Part II. In Fish and Fisheries. Houghton

Mifflin, Boston. HEATH G. W. (1956) The siphon sacs of the smooth dogfish (Mustelus canis) and spiny

dogfish (Squalus acunthius). Anat. Rec. 125, 562. HEATH G. W. (1960) The anatomy and growth pattern of the claspers and siphon sacs of

the spiny dog&h, Squalus acanthias Linnaeus, and the smooth dogfish, Mustelus canis Mitchill. Ph.D. thesis, Cornell University, Ithaca, N.Y.

HICKLINC C. F. (1930) A contribution towards the life-history of the spur-dog. r. mar. Biol. Ass. U.K. (New Series) 16, 529-576.

HOME E. (1809) An anatomical account of the Squalus maximus Linnaeus. Phil. Trans. R. Sot. Lond. 99, 206-220.

HOME E. (1810) On the mode of breeding of the ovoviviparous shark and on the aeration of the foetal blood in different classes of animals. Phil. Trans. R. Sot. Lond. 100, 205- 222.

HOME E. (1813) Additions to an account of the anatomy of the Squalus maximus. Phil. Trans. R. Sot. Lond. 103, 227-241.

JUNGERSEN H. F. E. (1899) On the appendices genitales in the Greenland shark, Somniosus microcephalus (Bl. Schn.), and other Selachians. Vol. II, Part 2. The Danish Ingolf- Expedition, Copenhagen. (Translated into English by Torben Lundbeck.)

LEIGH-SHARPE W. H. (1920) The comparative morphology of the secondary sexual charac- ters of elasmobranch fishes. Memoir I. J. Morph. 34, 245-265.

LEIGH-SHARPE W. H. (1921) The comparative morphology of the secondary sexual charac- ters of elasmobranch fishes. Memoir II. J. Morph. 35, 359-380.

LEIGH-SHARPE W. H. (1922) The comparative morphology of the secondary sexual charac- ters of elasmobranch fishes. Memoirs III, IV and V. J. Morph. 36, 191-243.

LEIGH-SHARPE W. H. (1924) The comparative morphology of the secondary sexual charac- ters of elasmobranch fishes. Memoirs VI and VII. J. Mmph. 39, 5.53-577.

LEIGH-SHARPE W. H. (1926) The comparative morphology of the secondary sexual charac- ters of elasmobranch fishes. Memoirs VIII, IX, X and XI. J. Morph. 42, 307-358.

MANN T. (1960) Serotonin (S-hydroxytryptamine) in the male reproductive tract of the spiny dogfish. Nature, Lond. 188, 941-942.

MATTHEWS L. H. (1950) Reproduction in the basking shark, Cetorhinus muximus (Gunner). Phil. Trans. R. Sot. Land. Series B, 234, 247-316.

MATTHEWS L. H. & PARKER H. W. (1951) Notes on the anatomy and biology of the basking shark, Cetorhinus maximus (Gunner). Proc. 2001. Sot. Lond. 120, 535-576.

PJITRI K. R. (1877) Die Copulationsorgane der Plagiostomen. Inauguraldissertation vorgeleget der Philosophischen Fakulttrt der Universitit Leipzig ziir Erlangung der Doktorwurde. Wilhelm Englemann, Leipzig.

PUTNAM F. W. & GARMAN S. W. (1874) On the male and female organs of the sharks and skates, with special reference to the use of the “claspers.” Proc. Am. Assoc. Adv. Sci. 23, 143-144.

SCHENSKY F. (1914) Tier- und Pflanzleben der Nordsee. Werner Klinkhardt, Leipzig. (As cited by Matthews, 1950.)

SMITH A. (1849) Illustrations of the Zoology of South Africa. Vol. IV: Pisces. London.

CLASPER-SIPHON SAC MECHANISM IN SQUALUS ACANTHIAS AND MUST!XUS CANIS 119

TEMPLEMAN W. (1944) The life history of the spiny dogfish (Squalus acunthias) and the vitamin A values of dogfish liver oil. Dept. nut. Res., Newfoundland. Research Bull. (Fisheries) No. 15, l-102.

VON BONQE C. (1945) Stages in the development of the picked or spiny dogfish, Squulus acanthius Linn. Biol. Bull. mm. b&l, Lab., Woods Hole 88, 220-232.

Key Word Index-iiktelus canis clasper-siphon; Squalm acanthias clasper-siphon; Squalus clasper mechanism; Elasmobranch clasper function; Elasmobranch siphon sac function; mating posture in sharks.

Date post:	10-Dec-2016
Category:	Documents
Upload:	heath
View:	217 times
Download:	0 times

The clasper-siphon sac mechanism inSqualus acanthias and Mustelus canis

Documents