270 The Reproduction and Metamorphosis of the Common Eel. 



in the testes here and there knots of spermatozoa. These spermato- 

 zoa are similar to those of the Conger vulgaris, and must be con- 

 sidered as ripe. As is well known, so advanced a stage of sexual 

 maturity has never before been observed in the Common Eel. This 

 appears to be due to the fact that the males hitherto examined had 

 not yet migrated into the deep water of the sea. 



Eels with big eyes taken from the depths of the sea were, before 

 the above facts were known, described as a distinct species under 

 the name of Anguilla bibroni (Kaup) and of Anguilla kieneri (Kaup), 

 not to be confounded with Anguilla kieneri (Giinther), which is a 

 synonym of Lycodes 'kieneri. 



In certain cloacae of ancient Rome which to-day are disused and 

 contain pure water, remarkable eels are found of a length of from 

 20 30 cm. of a grey colour, without trace of yellow, of male and 

 female sex, with enormous eyes and with more or less rudimentary 

 genital organs. They are individuals which, confined in a place 

 without light, have acquired prematurely one of the characters of 

 the bridal habit without a corresponding development of the genital 

 organs. These individuals are probably incapable of ulterior de- 

 velopment, as the condition of their genital organs seems to demon- 

 strate. 



Under the name Anguilla kieneri (Kaup) there have probably been 

 included some individuals which had acquired big eyes under con- 

 ditions similar to those described for the eels of these Roman cloacae. 

 From these and similar observations it clearly results that all the 

 European eels must be included under a single species, and this is an 

 important fact from another point of view, namely, that it destroys 

 an objection which might be raised against my conclusion with 

 regard to the development of Anguilla vulgaris from Leptocephalus 

 brevirostris, namely, the objection that Leptocephalus brevirostris 

 belongs not to Anguilla vulgaris, but to Anguilla kieneri, or to 

 Anguilla bibroni. 



To sum up, Anguilla vulgaris, the Common Eel, matures in th& 

 depths of the sea, where it acquires larger eyes than are ever observed 

 in individuals which have not yet migrated to deep water, with the 

 exception of the eels of the Roman cloacae. The abysses of the sea 

 are the spawning places of the Common Eel : its eggs float in the sea 

 water. In developing from the egg, it undergoes a metamorphosis, 

 that is to say, passes through a larval form denominated Leptoce- 

 phalus brevirostris. What length of time this development requires 

 is very difficult to establish. So far we have only the following 

 data : First, Anguilla vulgaris migrates to the sea from the month 

 of October to the month of January ; second, the currents, such as. 

 those of Messina, throw up, from the abysses of the sea, specimens 

 which, from the commencement of November to the end of July,. 



