666 



PISCES. 



Fig. 325. 



(1846.) In the Eel and the Lamprey we have the first appearance of 

 an ovary such as is common to the higher Yertebrata. It consists of a 

 very extensive vascular membrane covered by the peritoneum, and 

 attached in broad folds beneath the spine, extending nearly from one 

 end of the abdomen to the other (fig. 325). This viscus is not hollow, 

 neither has it any excretory duct ; so that naturalists were long at a loss 

 to explain how the ova of these creatures were expelled. 



(1847.) The extensive membrane 

 above alluded to, as is now sufficiently 

 well determined, produces in its sub- 

 stance the germs of the future pro- 

 geny; and these, as they become 

 mature, break loose from the nidus 

 wherein they were generated in the 

 interior of the peritoneal cavity of the 

 Eel, and float loosely in the abdomen. 

 There is no Fallopian tube as yet de- 

 veloped; but two simple orifices, 

 placed on each side of the anal open- 

 ing, serve to give exit to the count- 

 less eggs which thus escape into the 

 surrounding water. 



(1848.) The male organs of the 

 Lamprey and Eel, together with the 

 ovaria of the female, and the kidneys 

 and ureters, were accurately de- 

 scribed by Hunter in the Catalogue 

 of his Collection, and their form and 

 structure are illustrated by the pre- 

 parations and drawings still pre- 

 served in the College of Surgeons * ; 

 but in such fishes the testis of the 

 male so exactly resembles the female 

 ovary, that it was imagined even by 

 Sir E. Home that no males existed, or 

 that the females were themselves her- 

 maphrodite. According to Rathke f, 

 however, the testes of the male are 

 composed of solid granules, precisely 

 like the female ova ; and the secretion derived from them is in like 

 manner allowed to escape into the abdomen, from which it is expelled 

 through similar openings in the peritoneum. 



(1849.) In the Sharks and Rays we meet with a very important addi- 



* See Physiological Catalogue, vol. iv. pp. 48, 129, pis. 59 & 60. 



t Neueste Schriften der naturforschendcn Gosollschaft zu Danzig. Halle, 1824. 



Keproductive organs of the Lamprey 

 (Petromyzon marinus). 



