452 



Bashford Dean Memorial Volume 



In the male elasmobranchs, where fertilization is internal, the basal element of each pelvic 

 fin (basipterygium) is prolonged to form a stout backwardly directed skeletal rod supporting 

 a portion of the fin which is demarcated from the remainder and especially modified to 

 form a copulatory organ, the clasper. 



The clasper is rolled up in a manner resembling a scroll, so that instead of being a groove, 

 as it is usually described, it is a sufficiently closed tube along the greater portion of its length, 

 though the edges may not be and usually are not completely fused but overlapping. This 



tube is one along which spermatozoa pass, in- 

 jected by an apparatus, the siphon, which has 

 not hitherto been sufficiently well known and 

 investigated. 



The anterior proximal opening into this 

 scroU'Hke clasper groove or tube wiU be hereafter 

 known as the apopyle, the posterior, distal exit 

 from the same as the hypopyle. In the sharks 

 and dogfish the apopyle is close to the cloacal 

 aperture, while in the skates it is some consid- 

 erable distance posterior to it, an inch or more 

 in a moderately sized adult. 



Leading into the apopyle by a narrow ap- 

 erture, so as to communicate with the clasper 

 tube on either side, is a large cavity, the siphon, 

 a sac with extremely muscular walls, situated 

 immediately below the corium of the ventral sur- 

 face of the abdomen, frequently several inches 

 in length, close to the median Hne, and ending 

 bHndly, ha\'ing no communication \^nth the 

 coelom, and whose function and significance it 

 will be my endeavor to elucidate. 



In the skates, on the other hand, no such 

 hoUow sac is found, but its place is taken by the 

 clasper gland, contained in a sac which it com- 

 pletely fills. This gland has long been recognized, 

 but its containing sac does not appear up to the 

 present to have been demonstrated to be ho- 

 mologous with the clasper siphon of the sharks 

 and dogfish, which is but Httle known. 



Other accessory structures may be present 

 on the claspers, such as the spurs and the Uke 

 in Acanthias, but of these none attains such importance and is more frequently present 

 than a fan-like expansion at the distal end of the clasper, the rhipidion, whose function is to 



spray the spermatozoa in aU directions in a radiating manner The rhipidion attains a greater 



development in the skates than in the sharks. 



The manner in which the various parts of a myxopterygium, particularly the siphon, 

 function is described at length by Leigh-Sharpe (1920, pp. 247-251) in the case of 

 Scyllium catulus. 



Text-figure 97- 

 Pelvic fin region of a male Chla-mydosdachus: 

 A, ventral aspect; B, left lateral aspect. 



Cav., cavity; Cl.Gr., clasper groove; I.V., iliac vein; CJ.P., 



urogenital papilla; V.F., ventral fin; V.S., venous sinus. 



After Leigh-Sharpe, 1926, Fig. 4, p. 311. 



