LIFE HISTORIES 353 



condition undergoes a change in external characters : its skin, 

 previously yellow in colour, becomes silvery, its pectoral fin be- 

 comes black, and its eyes become larger. These differences, 

 especially the large size of the eyes, were distinctly recognisable 

 in the specimens obtained from the sea by Grassi. Eels in this 

 condition were frequently found in the stomachs of sword- 

 fish,, the capture of which is a regular industry off the coast of 

 Sicily. The great increase in the size of the eyes in eels in 

 the sea is in all probability an adaptation to life at considerable 

 depths, for it is well known that deep-sea fishes have large eyes 

 except in a few cases in which eyes are absent altogether. The 

 conclusion of the Italian investigators is that the eel spawns 

 naturally at a depth of about 200 fathoms. The coast of Sicily, 

 especially in the neighbourhood of Messina and the north-east 

 corner of the island generally, is very steep, so that the depth 

 of 200 fathoms is reached at a short distance from land. 



It seemed at first very improbable that the eels of the 

 British Islands and of north-western Europe would have to 

 migrate to a depth of 200 fathoms in the sea in order to spawn, 

 for the 100 fathom line passes a long way west of the English 

 channel, outside the west of Ireland and Scotland, to the north 

 of the Shetlands, and only approaches the coast along the south 

 of Norway. Consequently eels from the Thames or the Elbe 

 would have to travel all the way to the west of Ireland or to 

 the south coast of Norway before they reached the depths which 

 were supposed to be necessary for their reproduction by the 

 Sicilian naturalists. Evidence, however, has recently been 

 obtained that this extraordinary migration actually takes 

 place and that the elvers which ascend our rivers on the east 

 coast as well as on the west, or which make their way to the 

 waters of central Europe, were hatched in the great Atlantic far 

 beyond the 100 fathom line. The most important part of this 

 evidence is the result of the work of Johannes Schmidt, one of 

 the Danish naturalists engaged in the International Fishery 

 Investigations. 



One important problem in connection with the history of the 

 common eel north of the Mediterranean was to ascertain where 

 the Leptocephalus brevirostris was to be found. One specimen 

 of this form was identified by Giinther among the collections 

 of the "Challenger"; it was taken on the surface in the At- 



23 



