264 MR. T. SOUTHWELL ON THE REPRODUCTION OF THE COMMON EEL. 
The force of these observations will occur to us when we consider 
that, of our common freshwater Eel, three or four species have 
been described, all of which are mere variations, sexual or other- 
wise, and possibly only the natural stages in the normal progress 
towards maturity. The liabilities to error attending such a method 
will be still further illustrated when considering the multiplication 
of supposed species in the larval form of the same fish. The 
methods of investigation pursued by Grassi have been strictly 
scientific, and on the lines known as “ bionomics ” ; they were 
(1) anatomical, by comparison of the structures in all the various 
stages ; (2) natural, the finding in nature of all the required 
transitional stages ; and (3) experimental, by which means he 
followed, step by step, the metamorphosis in aquariums. 
Very little fresh light had been thrown on this obscure period of 
the life of the Eel between the time when I last addressed you 
and the discoveries of which I am about to speak. On the 
27th December, 1892, a female had been captured, twelve miles 
south of the Eddystone, the ova of which were apparently quite 
ready for exclusion, as recorded by Mr. Calderwood in the Ann. 
and Mag. of Nat. Hist. (vol. xii., sixth series, p. 35), thus 
confirming the belief that Anguilla spawns in salt-water and at 
considerable depths. But the first definite information of the 
discovery of the larval form was made known in a preliminary 
notice by Drs. Grassi and Calandruccio, in a journal called 
‘ Neptunia ’ in 1894, and this called forth a paper by 
Mr. J. T. Cunningham, which appeared in the ‘Journal of the 
Marine Biological Association’ issued in February, 1S95; but 
a further contribution by Professor Grassi was read at the meeting 
of the Boyal Society on the 19th November, 1896, communicated 
by Professor Bay Lankester, in which he gives a preliminary account 
of his four years’ continuous researches on the subject; this will 
be followed in due course by a more extended account of his 
interesting experiments. 
There has long been known to science a number of “strange, 
colourless, transparent, thin-bodied creatures, with blood destitute 
of red corpuscles,” which have by some been regarded as a special 
family of fishes, under the name of Leptoceplialidce or “ Glass-eels.” 
A considerable number of so-called species were recognised, only 
one of which was known to occur on our coast : this is figured and 
