384 G. B. GRASSI. 
measurement was recorded. Ina female eel, derived from the 
same source and purchased in the market, whose length was 
483 cm., the vertical diameter of the eye was 10 mm., and 
the transversal diameter rather more than 10 mm. These 
are not the greatest dimensions which I observed, and I con- 
clude from these facts that the bridal habit described by Petersen 
was not quite completed in his specimens, and that it becomes 
so only in the sea and at a great depth. In relation to these 
observations of mine stands the fact that the genital organs in 
the eel taken in the Messina currents are sometimes more 
developed than in eels which have not yet entered the deep 
water. Thus it has happened that male individuals have 
occurred showing in the testes here and there knots of sper- 
matozoa. These spermatozoa are similar to those of the 
Conger vulgaris, and must be considered 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 An- 
guilla kieneri (Gunther), which is a synonym of Lycodes 
kieneri. 
In certain cloace of ancient Rome which to-day are disused 
and contain pure water, remarkable eels are found of a length 
of from 20 to 30 em., 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 correspond- 
ing development of the genital organs. These individuals are 
probably incapable of ulterior development, as the condition 
of their genital organs seems to demonstrate. 
Under the name Anguilla kieneri (Kaup) there have 
probably been included some individuals which had acquired 
