SEXUAL CHAIL\CTERS — ELASMOBRANCH FISHES 371 



erectile tissue in the clasper and the least amount of cartilaginous 

 skeletal support; conversely, those species, e.g., Scyllium, which 

 possess no clasper glands do not rely on erection for the purpose 

 of copulation. 



The functions of the clasper gland would therefore appear to 

 be, at any rate in the Lamna type, the same functions as those 

 of the prostate, e.g., 1) lubrication and provision of a vehicle for 

 spermatozoa; 2) control of erection; 3) activation of the sper- 

 matozoa; 4) providing nourishment for the spermatozoa. Erec- 

 tion is most marked in Raia, Rhina, and Lamna. 



Considering Barrington's objection that the erection is due 

 rather to the katabolite of a muscle than to glandular secretion, 

 attention was particularly drawn in my preceding memoir to 

 muscle of a peculiar type in connection with the clasper gland of 

 Raia. In fact, we see that all the glands are well supplied with 

 muscular coats (contrast the rectal gland of Scyllium to be men- 

 tioned presently). It may be, then, that a function for this 

 specialized muscle is hereby indicated. 



Turning from the physiology to the embryological aspect of 

 these glands, I have endeavored in figure 9 to diagrammatize 

 their development so as to show their analogy and possibly 

 homology with the prostatic glands of mammalia. In these 

 sketches the proctodaeum and epidermal structures are indicated 

 by the broken lines, the urinogenital system, cloaca, etc., in 

 plain unbroken lines, and the accessory glands (prostate, Barto- 

 lini's, Cowper's, clasper) in solid black. 



Series A, nos. I to IV, shows ventral diagrammatic views 

 indicating the origin of the clasper gland from an invagination 

 of the side of the proctodaeum. IVa is IV in side view. 



Series B elucidates the isolation of the clasper gland from the 

 proctodaeum, by reason of the formation of its duct, or at least 

 of its peripheral end, from a groove on the medial aspect of the 

 clasper. 



Series C. In nos. I and II two stages are shown in the devel- 

 opment of the urinogenital system and accessory glands in 

 human embryos. No. Ill delineates the hypothetical primitive 

 condition of cloaca and proctodaeum with the areas from which 

 evaginations lead to the formation of accessory glands dotted in. 



