MARINE FOOD FISHES 125 



on the cruises of the Danish research boat Thor, and 

 is beautifully illustrated in the Science Museum at 

 South Kensington. 



The leptocephalus does not feed in the sea, and 

 consequently a reduction occurs in the length, depth 

 and weight of the fish. In this manner the flattened 

 leptocephalus is gradually transformed into the rounded 

 glass eel. The glass eel is shaped very much like the 

 elver, or young eel, but is still quite transparent. Later, 

 glass eels become pigmented, and, as elvers, during 

 the summer ascend our rivers in countless millions. 



During the voyages of the Thor, the greatest number 

 of leptocephali were found in the comparatively shallow 

 waters of the Continental shelf, off the south-west coast 

 of Ireland — consequently, this part of the Atlantic was 

 thought to be the spawning ground of the common eel. 

 But new light has recently been thrown on the wonders 

 of eel migration during the North Atlantic Expedition, 

 under Sir John Murray and Dr. Hjost, in 1910. Lepto- 

 cephali of the common eel, measuring about three inches 

 in length, were found north of the Azores undergoing 

 transformation. Others were taken south of the Azores 

 over a thousand miles from the mainland. These were 

 considerably smaller in size, and were not yet full grown, 

 and moreover were captured near the surface. It is 

 reasonable to assume, that the smaller specimens were 

 nearer the spawning grounds, and that these spawning 

 grounds were not off the Irish coast, but probably in 

 the centre of the Atlantic. 



