280 ANNUAL EEPORT SMITHSONIAN INSTITUTION, 1924 



the elvers come? And what are the still younger stages like, which 

 precede the "elver" stage in the development of the eel? It is such 

 problems as these that constitute the " eel question." 



The earliest possibilty of attacking this ancient problem scien- 

 tifically was afforded by the Italians Grassi and Calandruccio, of 

 whom the former published in 1896, in the " Proceedings of the 

 Eoyal Society of London," a report of their investigations at Mes- 

 sina, entitled : " The Reproduction and Metamorphosis of the Com- 

 mon Eel (Anguilla vulgaris) ^ 



Grassi and Calandruccio found that the elver stage is preceded by 

 a larval stage, inasmuch as they were able to show that the little 

 fish from the Straits of Messina, described by Kaup in 1856 as Lep- 

 tocephdlus brevirostris, is not an independent species, but the larva 

 of the eel. The larva is leaf-shaped, transparent as glass, and about 

 7I/2 cm. in length. By a process of metamorphosis it is transformed 

 into the eel-shaped elver, a reduction in both height and length tak- 

 ing place. 



This Italian discovery was of great importance; we had now 

 learned to know a stage still younger than the elver, and it did not 

 seem difficult from this to infer the remainder of the life-history of 

 the eel. Grassi was therefore justified in assuming that he had been 

 able "to dispel, in the most important points, the great mystery 

 which has hitherto surrounded the reproduction and the development 

 of the common eel {Anguilla vulgarisy (loc. cit., p. 261). Even 

 after the discovery of the larva, however, certain points still seemed 

 vague; one might yet ask, for instance : (1) ^Vliy were not the larvae, 

 like the elvers, found promiscuously about the shores of Europe, 

 but only in the waters of Southern Italy, especially the Straits of 

 Messina; and (2) why should we find in that water, not minute, 

 newly-hatched larvae, but only specimens already fully grown, or 

 nearly so, of about 7 cm. in length? 



Briefly, Grassi conceived the circumstances to be as follows: The 

 breeding grounds of the eel lie in the great depths of the sea — in the 

 abyssal region — which in the Mediterranean is not far from the 

 shores. In these depths the ova, suspended in the water, are devel- 

 oped, and here the larvffi live, normally without rising to the upper 

 water layers. The Straits of Messina, however, form an exception. 

 There are some peculiar currents here, that "tear up the deep-sea 

 bottom, which everywhere else is inaccessible" (loc. cit., p. 268); 

 hence, it is just in the Straits of Messina that these larvae are brought 

 to the surface and come under observation. 



This, roughly speaking, was the state of the eel question at the 

 commencement of the present century. In the year 1904 I was led 

 by chance to touch upon it myself. My very first investigations con- 

 firmed in every respect the Italian discovery of the eel larva and its 



