in the testes here and there knots of spermatozoa. These spermatozoa are sim ilar to those of the Conger and m ust be considered as ripe. As is well known, so advanced a stage of sexual m aturity has never before been observed in the Common Eel. This appears to be due to the fact th at the males hitherto examined had not yet m igrated into th e deep w ater of the sea.
Eels w ith big eyes taken from th e depths of the sea were, before the above facts were known, described as a distinct species under the name of Anguilla bibroni (K aup) and of Anguilla (K aup), not to be confounded w ith Anguilla (G unther), which is a synonym of Lycodes kieneri.
In certain cloacae of ancient Rome which to-day are disused and contain pure w ater, rem arkable eels are found of a length of from 20—30 cm. of a grey colour, w ithout trace of yellow, of male and female sex, w ith enormous eyes and w ith more or less rudim entary genital organs. They are individuals which, confined in a place w ithout light, have acquired prem aturely one of the characters of the bridal habit w ithout a corresponding development of the genital organs. These individuals are probably incapable of ulterior development, as the condition of th eir genital organs seems to demonstrate.
U nder the name Anguilla kieneri (K aup) there have probably been included some individuals which had acquired big eyes under conditions sim ilar to those described for the eels of these Roman cloacae. Erom these and sim ilar observations it clearly results th at all the European eels m ust be included under a single species, and this is an im portant fact from another point of view, namely, th a t it destroys an objection which m ight be raised against my conclusion with regal’d to the developm ent of Anguilla vulgaris from brevirostris, namely, the objection th a t Leptocephalus belongs not to Anguilla vulgaris, but to Anguilla kieneri, or to Anguilla bibroni.
To sum up, Anguilla vulgaris, the Common Eel, m atures in the depths of the sea, where it acquires larger eyes than are ever observed in individuals which have not yet m igrated to deep water, w ith the exception of the eels of the Roman cloacae. The abysses of the sea are the spawning places of the Common E e l: its eggs float in the sea water. In developing from the egg, it undergoes a metamorphosis, th at is to say, passes through a larval form denominated Leptocephalus brevirostris. W hat length of time this development requires is very difficult to establish. So far we have only the following data :—First, Anguilla vulgaris m igrates to the sea from the m onth of October to the month of J a n u a ry ; 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,
