SCYLLIUM CANICULA 249 



by numerous rounded projections, the ova, which are of different 

 sizes from quite tiny knobs like pin-heads up to yellow spheres 

 14 mm. in diameter, according to their state of development. The 

 pronephric tubules disappear, as has been pointed out, but the 

 funnels of the two sides remain and, moving ventrally, unite below 

 the oesophagus to form a single opening, the oviducal funnel. This 

 communicates by means of one of the tubules with the segmental 

 duct. Not merely does the pronephric duct persist, but it enlarges 

 considerably and constitutes the oviduct of the adult. The oviduct 

 is a thick-walled tube commencing at the funnel and passing 

 laterally on to the latero-dorsal wall of the coelom. A short way 

 along it swells out to form a marked ovoidal enlargement, the 

 oviducal gland, and then becomes constricted again. The walls of 

 the posterior half of the duct are thin, and the cavity enlarged to form 

 a hollow vesicle, the ovisac, in which the egg can be kept until laid. 

 The two oviducts open to the exterior by a single median aperture 

 on the dorsal wall of the cloaca, which in the young female is closed 

 by a thin membrane, the hymen. 



When ripe, the follicle ruptures and discharges the egg, now a 

 spherical mass about 14 mm. in diameter and loaded with yolk, into 

 the ccelom. It makes its way into the oviducal opening and passes 

 into one oviduct apparently the two oviducts function alternately. 

 In the top end of the tube it is penetrated and fertilised by a sperm 

 that has been introduced previously by the male fish, and it is also 

 provided with an albuminous coat. As it passes the oviducal gland 

 and beyond it is provided with a horny shell, the product of the 

 secretion of the gland. The shell is an oblong purse-shaped structure 

 with its long sides continued out as four horns tailing off as long 

 coiled threads, by means of which it is anchored to the seaweed when 

 laid. While in the oviduct the shell is of a pale yellow colour, but 

 after the hatching of the young and subsequent exposure it turns 

 black. Such empty cases belonging to Scyllium, or some other 

 Elasmobranch, are commonly cast up on the seashore and are 

 known as " mermaids' purses." 



The segmental duct in the male is functionless, but always remains 

 as a vestigial structure in the form of a tiny, almost invisible, solid 

 strand of tissue in the position of the oviduct in the female. Traces 

 of it may sometimes be seen in certain specimens. 



The testes are two elongated, soft bodies lying one on each side 

 of the middle line, and suspended from the dorsal wall of the coelom 

 by special folds of the peritoneum known as the mesorchia. Each 

 testis is attached to the front end of the corresponding mesonephros 

 by a number of fine tubules, the vasa efferentia, by whose agency 

 the sperms produced in the seminiferous tubules of the testis are 



