NATURAL HISTORY OF AMIA CALVA LINNtEUS. 95 



larvse have now strongly developed the habit of scattering and hiding upon mechan- 

 ical shock to the water. 



Before speaking in detail of the characteristics of these two periods, the habit 

 of swallowing air, a habit common to both periods, may be discussed. 



b. The habit* of swallowing air. — (Compare Fulleborn, '94.) This habit is 

 developed at a very early period, probably soon after the larvse leave the nest. I 

 have noted it in larvae of 10, 40, and 50 millimetres. The larva comes very slowly 

 to the surface, and appears to gulp in air; at the same time numerous small gas- 

 bubbles are seen at the surface of the water, as though gas were being ejected from 

 beneath the gill-covers. The larva then retreats rapidly from the surface with 

 quick movements of the tail. The larvse of a school often come to the surface for 

 air in groups of fifteen or twenty. When the school is crossing deep water and is 

 near the bottom this habit results in a vertical column of larvae going and 

 returning from the surface. In larvae of 50 millimetres, as the school moves through 

 the aquatic vegetation, itself quite concealed, the agitation produced by the larvae 

 as they come to the water surface, and by the bursting of gas-bubbles, produces a 

 distinctly audible rustling sound, and gives to the surface of the water an appear- 

 ance as though rain were falling. At this time the larvae are extremely active, 

 apparently never at rest, so that one is reminded of the incessant activity of a school 

 of porpoises. It is likely that this great activity of the larvae is associated with the 

 use of atmospheric air. 



The habit of swallowing air and emitting it again, at least in part, from beneath 

 the gill-covers is often observed in the male, especially at the spawning and some- 

 times while with the school of larvae (see also Wilder, '76). 



c. First period of larval history outside the nest. — (12 to 35 millimetres.) I have 

 described the development of the movements of the stationary swarm into those 

 of the progressive amoeba-like swarm, and of these into the fully progressive move- 

 ments of the school of larvae. The movements of the stationary swarms are, how- 

 ever, not lost, but reappear in the schools whenever these schools are at rest. The 

 school movement merely becomes the dominant one as the larvae grow older. 



When the school is undisturbed it moves along slowly with the male, the larvae 

 feeding as they go. If now the male be frightened away there is a characteristic 

 change in the behavior of the school. The following extracts illustrate this. After 

 the male had been frightened away the larvae did not scatter or hide, but remained 

 together in a swarm. " They soon began to circle, returning always at the end of 



* The term is used as indicating a constantly recurring form of behavior, and without attempt to distin 

 guish habit from instinct. 



