— 244 — 



mens ^ taken at Beloxi in U. S. in the middle of last century and preserved in the Zoological 

 JVIuseum at Copenhagen. These specimens measure 45, 47, 48, 49, 49, 51, 53 mm. and 

 are well-pigmented, so that they are undoubtedly metamorphosed and had perhaps already 

 begun to increase in length^. All these elvers are thus considerably shorter than the 

 smallest European- Atlantic specimen we have found, and further they are much thinner 

 and more slender. We see therefore that, just as the Leptocephali of the American eel 

 are evidently much smaller than those of the European, the same holds good for the 

 metamorphosed elver, or in other words: the American eel seems to metamor- 

 phose at a smaller size than the Europeans. 



We can now give the following summary of the investigations on the relation between 

 the European-Atlantic and the American- Atlantic eels: 



(1) The number of vertebrae differ; the females of the European eel having from 

 111 — 118 vertebrae (average 1 14726), the females of the American eel only from 104 — 

 110 vertebrae (average 107'012). Als no transition stages have been found in this regard, 

 at any rate hitherto, we have here a distinctive characteristic for the separation of the 

 eels occurring in North America and Europe. 



(2) The American eel is shorter and plumper in form than the European and the caudal 

 fin is often more rounded. Similarly the origin of the dorsal fin is as a rule further back 

 than in the European eel, but these characters undergo so much variation within the two 

 species, that we cannot always rely upon them alone for the separation of the two. 



(3) Metamorphosis in the American eel seems to occur at a smaller size than in the 

 European-Atlantic, as both the Leptocephali and the metamorphosed elvers seem to be 

 much smaller in the former than in the latter. (The average length of the, European- 

 Atlantic Leptocephali was found to be ca. 7574 ^"^- [^65 specimens] and is 48 mm. for 

 the American [2 specimens of 47 and 49 mm.], both for specimens in Stage l.) But new 

 investigation of the American eel is necessary, as only 2 specimens of its Leptocephalus 

 stages are known as yet, before we can determine anything in this regard with certainty. 



For the purpose of expressing an opinion as to whether the American ^4. clirysypa 

 is specifically distinct from the European (and African?) A. vulgaris, we still lack invest- 

 igations on the number of vertebrae in specimens from the southern parts of both regions, 

 as it is quite conceivable that such an investigation would give uniform transitions between 

 both. For the time being we must be content to demonstrate, that the eels of Northern 

 America and Northern Europe are very distinct in several characteristics, especially in the 

 number of vertebrae, which is in good agreement with the supposition that the great depths 

 of the Atlantic form a barrier between the stock of eels on both sides of the ocean. 



smaller than the European, as they were found in the Atlantic off the North American coast, where the temperature 

 of the water is, I think, not higher than in the Atlantic off the British Isles from which our Leptocephali come. 



1 These have already been described by C. G. JOH. Petersen (1905, I. c. p. 3) who counted the vertebrae 

 of the specimens. 



2 This is also indicated by the fact, that the alimentary canal contains food in most of them, and it is 

 therefore reasonable to suppose that they have been even smallei'. The same is the case with some specimens, 

 which 1 received later from U. S. National Museum, Washington D. C. and which, come from different places 

 in the U. S. e. g. from Wilmington, North Carolina (Length: 45, 48, 48, 52, 53 mm.) and from Woods Hole, Mass. 

 (Length: 52, 53, 53, 53, 54, 54, 55, 55, 57, 58, 58, 59, 59, 59, 60, 61, 61, 62, 63 mm.). (Note added during press.) 



3 On the other hand the adult condition of A. chrysypa does not seem to be smaller than in A. vulgaris, 

 as according to Jordan & Evermann I. c. p. 348 it reaches a length of 4 or 5 feet. 



