r.v.i: Two 



E V O L U T I O N 



August, 1929 



The Life Story of An Eel 



Bx PAL'LIXE H. DEDERER 



'T'HE most famous person undoubtedly to inquire 

 into the family antecedents of the eel was Aristotle, 

 who left a record of his opinion that eels have no sexes 

 or eggs, and that they arise from the entrails of the 

 sea. Later speculation.'^, less negative, but no nearer 

 the irutli, derived them from snakes, worms, or beetles, 

 and — the latest suggestion, emanating from New Eng- 

 laiul- vven frcm clam.',. 



Why should it 

 be so difficult to 

 get the facts re- 

 garding the de- 

 velopment of 

 these bizarre 

 fishes? Anyone 

 who has visited 

 a fish hatchery 

 has probably 

 seen tnousands 

 of tiny trout de- 

 veloping from 

 eggs laid and 

 fertilized in the 

 waters of the 

 hatchery. B u t 

 only four years 

 ago did anyone 

 ever see the egg 

 of an eel, and 

 only one person has ever studied its development. 

 Now the matter is simplicity itself. All anyone need 

 do is to join a deep-sea exploring expedition, embark- 

 on a yacht equipped with the last word in scientific 

 apparatus, and proceed to a region of the Atbrntic 

 (Jcean southwest of Bermuda — the famed Sargasso 

 Sea where, in 1925, William Beebe and his company 

 of scientists reveled in their "Arcturus Adventure." 



Then you may watch the nets go down and scooo up 

 quantities of the surface life of the sea, or planktfju. 

 In this oozy "sea soup" may be found the larvae of 

 eels, varying in size from a quarter of an inch to tiiree 

 inches in length, thin as a willow leaf, and of about 

 the same shape. Dr. Beebe described them as "mother- 

 of-pearl eyes swimming round by themselves," the 

 body being perfectly transparent. The finding of the 

 larvae was not a new discovery, for Dr. Jobs. Schmidt 

 of Denmark had worked out the astounding migration 

 path of the larvae and their metamorphosis into eels, 

 publishing his results just before the Arcturus Ex- 

 pedition set out. But neither he nor anyone else knew 

 what the larvae came froin. 



To unravel this mystery, ask the expert on larval 

 fishes for a microscope and one of those pin-head dots 



Development of eel: At first it shrinks 



in size, then assumes adult shape and 



starts to grow 



of living stuff dredged up from the sea depths, which 

 are engaging her attention. Then, after a few days of 

 more or less constant study — and let us hope the ship 

 is not pitching too much — you may observe, as did 

 Marie Poland Fish, the tiny dot actually transform 

 into a larval eel. This discovery shows the importance 

 of being in the right .place at the right time. The right 

 place — and the only place — to answer this question 

 about eels, is in mid-Atlantic, the only region where 

 our eels breed. Thus with a few accessories, like 

 niiscroscopes, a ship, patience, scientific training, and 

 immunity from mal-de-mer, the question that perplexed 

 Aristotle is answered. Simple enough ! 



Now the whole story is known. American and Euro- 

 pean eels have the same breeding ground, the sea near 

 Bermuda. The larvae drift northward in the currents 

 of the Gulf Stream, changing from leaf-like creatures 

 into small rounded eels, or elvers. The American 

 species seek the various rivers along the eastern shore 

 of the United States, and swarm up-stream in great 

 numbers, even wriggling over grass on rainy nights to 

 reach the land-locked pKjnds in which they mature. In 

 the fall of the year, the adult eels migrate from inland 

 waters to the sea, traveling months before they reach 

 the Atlantic breeding grounds, there to begin anew the 

 cycle of development, and to die immediately after 

 spawning. 



European eels, migrating northward in the same 

 ocean currents, take three years instead of one to meta- 

 morphose. They are therefore not ready to ascend 

 ri\ers when they near our shores and are carried on 

 north-easterly until they reach the shores of Europe. 

 Phere, as elvers, they ascend the streams and rivers. 

 Dr. Schmidt, in his report on The Breeding Places of 

 the Eel, states that eels have been taken in waters in 

 Switzerland at an altitude of 3,000 feet above the sea. 

 He points out that although extensive migrations of 

 fish are not unusual, the eels are really related to salt- 

 water fishes, and "the remarkable point in their life 

 history is not so much the fact of their migration out 

 to sea to spawn, as in their leaving it in order to pass 

 their period of growth in an environment so unusual 

 for muraenoid fishes as fresh water." 



The basis for the idea that eels arise from clams, al- 

 ready referred to, is probably the observation that 

 clams often have a transparent gelatinous rod, about 

 one inch and a half long, protruding from a break in 

 their tissues. This rod is eel-like in form and size, and 

 like the undeveloped eel is also transparent. It is a « 

 secretion from the stomach of the clam called the 

 crystalline style. Its function was not definitely known 

 until Dr. Thurlow Nelson of Rutgers University in 

 1925 explained its importance in aiding to separate 

 the food materials from sand in the digestive tract of 

 the clam. 



