DEAN, BEHAVIOR OF THE EEL DURING TRANSFORMATION S25 



are now seen. The patch of jugular villi is reduced in size. The be- 

 havior of the young fish is eel-like. It remains motionless for longer 

 periods, occasionally lifting and turning its head, and there are pro- 

 nounced movements of its opercula. 



September 22. Larval coloration is apparent in the white spots above 

 and below the tail. In general the advances are clearly in the direction 

 of the mature eel. The vertebrae are conspicuous; the visceral wall be- 

 comes opaque; the jugular larval organ is represented by a clump of 

 scattered filaments; the gill region is more conspicuous (Fig. 7); the 

 gill arches show the red lamellae, expand broadly and contract; the 

 mouth opens wide; there is no movement in the neck region; the pec- 

 toral fins function; and the swimming is snake-like, with more effort 

 than propulsion, i. e., slipping, unlike the precise movements of earlier 

 stages. 



September 26. From now onward, the changes are less noticeable. 

 Larval coloration is retained, e. g., in the light colored spots. The trunk 

 is opaque, even in the gill region. 



September 28. At this stage, the last trace of the larval jugular organ 

 was noticed. The body is thickened; the white spots have disappeared 

 (Fig. 8). 



October 2. The last stage recorded (Fig. 9). Transformation is 

 practically complete. Measurements of this contrasted with the earliest 

 stage show a surprising shrinkage in the length and height of the young 

 eel, — more exaggerated even, than in the cases described by Grassi. In 

 the present instance, the young fish is about one-half the length of the 

 earliest stage, and one-third of its height, after a growth period of about 

 three weeks. It is another example of the paradox that development 

 may be accompanied by considerable diminution in size. 



Especially interesting in the foregoing transformation is the rapidity 

 with which the behavior of the young eel changes. This is not brought 

 out in adequate detail in the present note, but it may be said that the 

 observer could not but feel that the larva behaved like an animal suite 

 of a different species from the one of the days before, or of the days 

 following. This state of affairs predicates, obviously, kaleidoscopic 

 changes in elements of the central nervous system, and astoundingly 

 delicate and rapid adjustments; but whether these can be actually de- 

 termined, i. e., in the physical characters of the cells of brain and cord, 

 must yet remain an open question. It can be solved only when an 

 abundant material of Leptocephalus falls into the hands of a specialist 

 who can bring to his aid the latest neurological technique. 



