NATURAL HISTORY OF AMIA CALVA LINN^IUS. 87 



F. With the shrinking of the heavy yolk-sac and the atrophy of the adhesive 

 organ the individuals gradually acquire progressive movements which are well 

 marked at the end of twelve to sixteen days. These are effected by the rapid 

 vibration of the pectorals and of the heterocercal caudal, and are intermittent in 

 character, intervals of rapid vibration alternating with shorter intervals during 

 which the fins are at rest or nearly so and the fish merely forges ahead. The pro- 

 gressive movements at this period resemble in their intermittent character those 

 of the adult brook lamprey. By the time the larvae are ready to leave the nest, 

 the intervals of rest have been much shortened and the vibratory movements are 

 nearly continuous. 



G. Swarms of larvae are formed and progressive movements are developed 

 within a few hours. Six nests containing larvae about ready to leave the nest were 

 examined on the morning of May 8 and the following conditions found: "The 

 larvae are usually bunched together, often in a dense mass with many of the individ- 

 uals hidden in the fibrous roots of the nest bottom." In nests containing some- 

 what younger larvae the masses or swarms are stationary and the individuals com- 

 posing them are still using the adhesive organ. From time to time the individuals 

 free themselves, swim back and forth through the swarm, then become again 

 attached. In other nests the swarms are also stationary, but the individual fish 

 are no longer using the adhesive organ, but are in continuous movement back and 

 forth within the limits of the swarm. Such swarms are composed of larvae about 

 9 millimetres long. 



In the afternoon I returned to some of these nests. In some of them the 

 larvae were no longer to be found, in others they were in the same condition as in 

 the morning, but in one the larvae were nearly ready to leave the nest. None of 

 them were using the adhesive organ. "They swim together in a swarm which 

 moves in a generally circular direction about the edge of the nest or just outside it. 

 The larvae, though not progressing continuously as individuals, form a swarm which 

 nevertheless progresses, one way and another, with many internal irregularities. 

 The movement reminds one of the indefinite flowing movements of an Amoeba, 

 in which pseudopods are put out this way and that and often withdrawn, but the 

 animal as a whole progresses definitely." These larvae were 11 millimetres long. 

 How a stationary swarm may thus become progressive I was able to observe at 

 another time in a nest which had been deserted by the male and which, in order to 

 protect it from marauding fish, had been fenced in by placing a frame of boards about 

 it so as to form a square enclosure five metres on each side. The larvae were in 

 several masses. In one of these "the larvae formed a dense swarm four inches in 



