390 M. C. Robin on the Sexual Differences of Eels. 



their nuclei, which are set free, and may or may not become 

 slightly irregular. 



A deferent canal, about 1 millim. wide, with delicate walls, 

 runs along tlie adherent inner or dorsal margin of each testis 

 from one end to the other. These unite in a single cavity or 

 seminal vesicle at the level of the cloaca. The seminal vesicle 

 opens into the urethra by the genital pore, and by the urethra 

 almost immediately into the cloaca. The wall of this spermi- 

 duct is at the utmost ^ millim. in thickness. It is composed 

 of an inner layer of longitudinal, and an outer one of circular 

 fibres ; both of these, at the base of the lobes and a little upon 

 their outer surface, entangle their bundles with those of the 

 envelope of the male organ. These layers are formed of 

 cellular tissue evidently mixed with smooth muscular fibres. 



A single series of small polyhedric epithelial cells lines the 

 inner surface of the deferent canal. Adherent to the inner 

 border of all the delicate testicular lobules, it is thus lodged 

 within the peritoneal fold attaching the testis to the swimming- 

 bladder and the upper part of the abdominal walls. 



As will be seen, with regard to the determination of the 

 male sex of the Eels, we had to compare the well-known 

 female generative organs with their homologues in the nume- 

 rous individuals or groups of individuals which have external 

 characters somewhat different from those of the most widely- 

 distributed of these fishes. 



The absence of ova in the one set, their presence at all times 

 in the others, yjj to j^^ millim. in diameter, so easily ascer- 

 tained, might have furnished a demonstration, .^even without 

 the comparison of the structure of the organ without ovules 

 with the testis of other fishes. 



These comparisons ought certainly to have been made 

 before any investigation tending to prove the existence of an 

 exceptional hermaphroditism, or indeed before imagining, 

 without any previous study of the evolution of the ovary, that 

 the organ described as the testis is only an ovary which has 

 not arrived at its complete development. 



The testicular structure in the organ of certain eels which 

 is the homologue of the ovary of the others being incontest- 

 able, all that has been said, even within the last few years, of 

 this hermaphroditism, and of the resemblance in this parti- 

 cular between the Eels and the Serranidge, need no longer be 

 discussed. 



We may add that in the Murcence {M. Jielena, L.) the gene- 

 rative organs constitute no exception to what they are in other 

 osseous fishes. The males of the Congers, or rather the place 

 of their ordinary sojourn, alone remain to be discovered. 



