286 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1924 



morphosis, whereas in August and September the majority were 

 undergoing the process. It appears, then, that there is a certain 

 periodicity in the occurrence of the larvae; the full-grown larval 

 stages are met with in spring and early summer, metamorpliosis 

 takes place in the autumn, and the elvers appear in winter and 

 spring. With the abundance of material at my disposal, I found 

 occasion to make a closer study of the metamorphosis, and was able, 

 by means of numerous measurements, to ascertain that the larvae, 

 during the process of metamorphosis, are reduced in length about 

 1 cm., from about 75 mm. in June, 1905, to about 66 mm. in May, 

 1906, and in weight to less than a quarter of that before metamor- 

 phosis (pi. 3). The fully metamorphosed small eels, averaging 

 about 61/2 cm. in lengih, which occur in Europe in early summer, 

 must, therefore, be presumed to be about a year older than the larvae 

 found at the same time in the Atlantic west of Europe, which are on 

 an average about 7I/2 cm. long. 



Our investigations in 1906 to the west of France showed that the 

 larvae occurred even over the greatest depths, over 5,000 meters; we 

 found, moreover, that they were always distributed in a particular 

 manner, the specimens which had not yet commenced metamorphosis 

 being taken farther from the coastal banks than the older ones, which 

 were undergoing the process. This led me to point out the prob- 

 ability that the breeding grounds of the eel were situated out in the 

 ocean far from the coasts (1909) ^ a supposition which was to be 

 further supported in the very next year after it had been advanced, 

 by the 'appearance of new material of eel larvae from the open Atlantic. 



In a study published almost at the same time (1909)^ on the " Dis- 

 tribution of the Fresh-water Eels throughout the World," I drew 

 attention to the fact that the distribution of the eels in the Atlantic 

 area distinctly coincides with the periphery of the great anticyclonic 

 circulation of the water masses in the North Atlantic. 



The new m'aterial referred to — eel larvae from the open Atlantic 

 Ocean — was derived, partly from the cruise of the Norwegian steam- 

 ship M. Sars in the Atlantic, June-July, 1910, partly from some old 

 collections of Leptocephali which had lain for many years unex- 

 amined at the Zoological Museum in Copenhagen. Before proceeding 

 to this new m'aterial, I would call to mind that the eel larvae — nearly 

 800 in all— which I had taken on board the Thor in 1905 and 1906 from 

 the waters west of Europe, averaged about Ti/o cm. in length. The 

 largest measured 88 mm. and the smallest 60 mm. (see graph, fig. 2, 



6 " Remarks on the Metamorphosis and Distribution of the Larvae of the Eel {Anguilla 

 vulgaris)" (" Meddelelser fra Kommissionen for Havundersogelser, Serie Fiskeri," Vol. 

 Ill, No. 3, Copenhagen, 1909). 



" On the Distribution of the Fresh-Water Eels (Anguilla) throughout the World "' 

 ({bid.. No. 7, 1909). 



