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, 
