SEXUAL CHARACTERS — ELASMOBRANCH FISHES 



215 



apopyle. The gland becomes more and more twisted out of 

 one plane in each succeeding genus. A transverse section 

 (fig. 16) reveals, in each case, that its histological structure is the 

 same as in Raia. Owing to their larger size, the glands only are 

 shown in section in this memoir; the relation of the gland to the 

 siphon sac is seen in Memoir I, figures 10 and 11. 



Fig. 16 Torpedo marmorata, a transverse section of the clasper gland (hae- 

 malum-eosin) . 



TRYGON PASTINACA 



The sting-ray 



The specimen considered (fig. 17) was taken in the Bay of 

 Biscay in March, 1892. It exemplifies the two-spined stage, 

 and measures 69 cm. in length, and 40 cm. at the greatest breadth 

 across the pectoral fins. The flesh of the inner edge of the clasper 

 is drawn up into a pronounced ridge-like fold, the pent. The 

 hypopyle is very close to the apopyle, and there the clasper-gland 

 duct debouches. The rhipidion is pronounced, and is hard and 

 shell-like with an edge like a knife-blade, so that, in spite of an 

 epidermis over it, it is easy to cut the finger on it. The clasper 

 gland is as in Torpedo (fig. 18). 



