290 LECTURE XII. 



into numerous folds, whicli are transverse in the Cod and Salmon*, 

 oblique in the Mackerel, and longitudinal in some other fishes. In 

 the osseous fishes that retain and hatch their ova the stroma does 

 not extend to the posterior part of the ovarian sac, but this serve? as 

 a kind of uterus, and contains an abundant albuminous secretion at 

 the season of the internal incubation. The viviparous Blenny 

 { Zoarces), the Anableps, the Poecilia, and some Siluroids are ex- 

 amples of ovo-viviparous osseous fishes, and at the same time 

 manifest naturally, what occurs as a rare adnormality in higher Ver- 

 tebrates, viz. ovarian gestation. In the Plaice and other Pleuro- 

 nectidffi the parallelism between the male and female organs is so close, 

 that the ovaria also escape from the abdomen, and become lodged 

 in greater or less proportion in sub-cutaneous scrotal cavities above 

 the basis of the anal fin. f 



In the Lamprey the short and narrow lateral infundibuliform 

 passages behind the rectum, into whicli the ureters open, and which 

 terminate in the peritoneal outlets {Jig- 74. e, I), have been compared 

 to short oviducts. In the Sturgeon actual oviducts are continued 

 from the ureters forward, which open by wide infundibular apertures, 

 comparable to the ' morsus diaboli' of anthropotomy, into the 

 general peritoneal cavity, and receive the ripe ova as they burst from 

 the ovarium. The urine is prevented from regurgitation into the 

 serous cavity through the same passage, by a valve which only allows 

 the passage of the ova backwards into the common uro-genital 

 duct. The higher grade of the sexual organisation of the female 

 Plagiostome, as compared with the cartilaginous Ganoid fish, is ma- 

 nifested chiefly by modification of the oviducts ; they are always two 

 in number, and distinct from one end to the other, but are brought 

 into close proximity, or coalesce at both ends : they are ahvays 

 distinct from the ureters, which terminate on the prominent urethral 

 clitoris, between the oviducal outlets. Different parts of the oviducts 

 are modified, moreover, for special functions, superadded to that of 

 effecting the safe transit of the generative product. The ovaria 

 of Plagiostomes {fig- 75. a) are relatively much smaller than in other 

 fishes, of a more compact form, and confined to the fore part of the 

 abdominal cavity : they are sometimes blended into a single body. 

 The stroma is not spread over the walls of a cavity, but is collected 

 into a loose cellular mass, circumscribed by a fibrous membrane, and 

 suspended by a duplicature of peritoneum to the dorsal parietes of the 

 abdomen, at the sides of the oesophagus. The ova are much fewer in 

 number than in the 'roe' of osseous fishes, and are seen in different 



* In the Salmon the free surface of the stroma is exposed, 

 •)■ xLiii. V. pi. 4. fig. 1. 



