THE AGE OF FISHES 195 



their movements at sea directly, the evidence was indirect. 



From the contents of plankton nets towed in various parts 

 of the Atlantic Ocean aboard the Thor and Dana, Schmidt 

 found that younger and younger stages of the tiny eels could 

 be traced farther and farther back to the deep central part 

 of the North Atlantic Ocean southeast of Bermuda. Trans- 

 parent eggs about the size of a pea are found there in the 

 spring about 500 feet below the surface, so that mating prob- 

 ably takes place near the deep-sea floor beneath. When the 

 flat, leaf-like eel larva is first hatched it is only a quarter of an 

 inch long. It is so different from the adult eel in appearance 

 that when first discovered it was thought to be a new and 

 altogether different fish, and was therefore named "leptoceph- 

 alus.'' From the time of hatching these bizarre creatures grow 

 slowly, and meanwhile travel on the long path toward fresh 

 water. As a result of numerous measurements Schmidt was 

 able to show that the baby eel takes three years to reach 

 European waters. The American eel, a very close relative, 

 breeds close by and to the southwest of the spawning area 

 of its European cousins, but its journey to the American rivers 

 takes only a year. 



We cannot be sure, but it seems likely that the newly- 

 hatched leptocephalus rising part way to the surface is caught 

 by the Gulf Stream and thus carried in a slow easterly drift 

 to the European shores. By the time it reaches there it has 

 become of an age when it is strongly attracted by the fresh 

 waters draining out of rivers, and it is old enough to swim 

 against tide and current into the estuaries. Perhaps the rise 

 of the American leptocephalus to a particular depth at a 

 particular time places it within the grasp of somewhat differ- 

 ent layers of water flow, so that when it reaches the time 

 to change into an elver the ocean drifts have brought it near 

 American shores. We can only surmise, for the complete 

 evidence is still to be collected. 



During the long transatlantic crossing the young eel grows 



