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THE AMEBIC AN NATURALIST [Vol. XLTI 



and are found in association with typically pelagic organisms 

 such as Salpa, Cymbulia and Phronima, as well as the young of 

 other pelagic or deep-sea fish, among which are five additional 

 species of "Leptocephalus." They have also the leisurely move- 

 ments characteristic of many pelagic animals. 



The pre-Leptocephalus stages of the eel are as yet wholly un- 

 known. The earliest season of investigation has been the month 

 of May and at this time the pelagic larva' are found during the 

 day in greatest abundance in levels at a depth of about 100 m., 

 but rise to the surface levels at night. This distribution of the 

 youngest known stages leads Dr. Schmidt to surmise that the 

 eggs of the common eel are bathypelagic. and that the larvae as 

 they develop rise to the upper levels. 



The pelagic larva? appear to reach the height of the larval 

 stage of development in June and ceaso active feeding, but do not 

 as yet show the regressive phenomena which characterize the 

 period of metamorphosis. They have also reached their maxi- 

 mum larval size 75 (60-88) mm. Both upper and lower jaws 

 are equipped with long slender grasping teeth. No pigment is 

 found in the body except in silvery iris of the eye. The digestive 

 tract at this time extends through about two thirds of the length 

 of the body. 



The larval stage is followed by a long period of metamorphosis 

 during which the form of the body changes from that of a color- 

 less ribbon-like band to the pigmented cylindrical type with 

 differentiated head and tail. The pelagic mode of life is aban- 

 doned and the young eels or elvers adopt the bottom habitat 

 in shallow coastal and fresh waters into which they have mi- 

 grated from the open sea. This period of metamorphosis occu- 

 pies the entire year or more, during which no food is taken. The 

 body gradually decreases in size as the metamorphosis proceeds, 

 diminishing from an average length of 75 millimeters in the high 

 seas in June to 65 millimeters a year later in coastal waters. The 

 digestive tract shortens during this period from two thirds to 

 one third of the total length of the body. Mandibular and 

 vomerine teeth appear and dermal sense organs develop about 

 the head. 



During this long period of metamorphosis the Leptocephalus 

 larvae migrate slowly from their habitat above the 1,000-meter 

 line shoreward. According to the recent summary of observa- 

 tions published by Professor Gilson, they reach the coasts 

 Spain and Ireland in October-December, and the wes1 



