394 READINGS IN BIOLOGICAL SCIENCE 



After years of tireless effort he was able, through this method, to fix the 

 breeding and spawning grounds of the European eel {Anguilla vulgaris) 

 and the American species {Anguilla rostrata) within the latitudes 20-30 de- 

 grees north and longitudes 60-78 degrees west. He further established the 

 fact that the European beds overlapped those of the American species. 



But this discovery uncovered but one phase in the life cycle of the eel. 

 During the period of growth in the waters of their home continent, both 

 males and females are a uniform green to yellowish-brown above, shad- 

 ing to a pale dirty white beneath, and are called "yellow eels." When the 

 migratory instinct asserts itself at the breeding stage, which is in the autumn 

 when they are between the ages of seven and fifteen years, the sides of 

 their bodies take on a metallic sheen and their backs become a deep black. 

 This is their breeding dress, and they are then known as "silver eels." 



Upon assuming this dress certain other marked changes take place in 

 the females. Their snouts become sharp, the eyes larger, and the pectoral 

 fins, just back of the gill slits, more pointed than usual. Although they have 

 been voracious eaters all of their lives they cease feeding at this time, and, 

 leaving the lakes and rivers in which they have lived, move downstream 

 to the sea. But while these visible changes have been taking place, it is not 

 until after they have reached salt water that the ovaries mature. In fact 

 no perfectly ripe female eel and only one ripe male has ever been seen. 

 Upon arriving in the bays and estuaries of their home shores they are joined 

 by the mature males that have been living there, and together they start 

 the journey back to their birthplace over 2500 miles distant. 



It is not known how far below the surface they swim, but somewhere 

 beyond the continental shelf they pass from the range of observation. 

 Neither is it known how long it takes them to reach their destination, but 

 it has been estimated that the eel requires about six months to make the 

 crossing, swimming at the rate of one-half mile an hour. As the migration 

 from the European continent begins in early autumn, and spawning starts 

 in early spring at the breeding grounds, this estimate of the period of time 

 seems to be justified. 



Upon arrival at the breeding grounds, the European species find that 

 they must share it with their American cousins whose beds overlap their 

 own, but extend westward from it. From Labrador southward to Panama 

 and the West Indies, the "silver eels" from America have journeyed to 

 the rendezvous in from one to two months after reaching salt water. Hun- 

 dreds of fathoms below the seaweed-clogged surface of this tropical sea 

 the eggs of both species are spawned; the females producing from 5-20 

 million tiny eggs, transparent and almost colorless. 



Spawning begins in late winter or early spring, and a week or so after 

 fertilization the eggs are hatched and larvae of both species begin hfe with 

 a length of about one-fourth inch. Ribbon-like in shape and so transparent 

 that newsprint can be read through their bodies, they float for a time from 



