THE VASA EFFERENTIA. 489 



In the remaining parts of the excretory organs the two species 

 of Scy Ilium resemble each other very closely. 



As may be gathered from Prof. Semper's monograph, the 

 excretory organs of Scyllium canicula are fairly typical for Elas- 

 mobranchs generally. The division into kidney and Wolffian 

 body is universal. The segmental openings may be more 

 numerous and larger, e.g. Acanthias and Squatina, or absent in 

 the adult, e.g. Mustelus and Raja. Bladder-like swellings of the 

 Wolffian duct in the female appear to be exceptional, and 

 seminal bladders are not always present. The variations in the 

 ureters and their openings are considerable, and in some cases 

 all the ureters are stated to fall into a single duct, which may be 

 spoken of as the ureter par excellence 1 , with the same relations 

 to the kidneys as the Wolffian duct bears to the Wolffian body. 

 In some cases Malpighian corpuscles are completely absent in 

 the Wolffian body, e.g. Raja. 



The vasa efferentia of the testes in Scyllium are very typical, 

 but there are some forms in which they are more numerous 

 as well as others in which they are less so. Perhaps the vasa 

 efferentia are seen in their most typical form in Centrina as 

 described and figured (PI. XXl) by Professor Semper, or in Squatina 

 vulgaris, as I find it, and have represented it on PI. 20, fig. 8. 

 From my figure, representing the anterior part of the Wolffian 

 body of a nearly ripe embryo, it will be seen that there are five 

 vasa efferentia (v. e) connected on the one hand with a longitudinal 

 canal at the base of the testes (n. t) and on the other with a 

 longitudinal canal in the Wolffian body. Connected with the 

 second longitudinal canal are four Malpighian bodies, three 

 of them stalked and one sessile ; from which again proceed 

 tubes forming the commencements of the coils of the anterior 

 segments of the Wolffian body. These Malpighian bodies are 

 clearly my primary Malpighian bodies, but there are in Squatina, 

 even in the generative segments, secondary Malpighian bodies. 

 What Semper has described for Centrina and one or two other 

 genera, closely correspond with what is present in Squatina. 



1 I feel considerable hesitation in accepting Semper's descriptions of the ureters 

 and their openings. It has been shewn above that for Scyllium his statements are 

 probably inaccurate, and in other instances, e.g. Raja, I cannot bring my dissections to 

 harmonise with his descriptions. 



B. 32 



