98 NATURAL HISTORY OF AMIA CALVA LINN^US. 



of remaining in concealment, the males of these swarms could not be positively identi- 

 fied after May 20, that is, after the larvse were 32 millimetres long. 



The "green-spot" school found in the hummocks on May 10 was found there 

 on May 16 and 18 within 75 metres of the same spot. On May 18 the school of the 

 "green-spot" male, which had heretofore consisted, as is usual, of larvse of nearly 

 the same size, was found now to consist of larvse of two very different sizes, 17 and 

 23 millimetres. Evidently two swarms had here become commingled. 



The "ring" school was found on May 16, and on June 5 was again found enter- 

 ing the basin, a migration of 400 metres. 



From the above it appears that each school is local, probably not going more 

 than a hundred metres from the nest until the larvse are about 30 millimetres long. 



The larvse of all ages show a tendency to keep in the shade, and this becomes 

 more pronounced as they grow older. Larvse 18 millimetres long, exposed in a glass 

 dish to the diffuse light of a window, show no tendency to go either toward the light 

 or from it. If now one-half the dish (a 9-inch bacteria-dish) be covered with black 

 cloth and so placed that the rays from the window strike it in the direction of the 

 plane separating the light and dark halves, it is found that on the average about 

 twelve times as many larvse are to be seen on the dark side of the dish as on the 

 light side. The same reaction, but more pronounced, is noted in larvse of 35 

 millimetres. If a nine-inch bacteria-dish containing such larvse be placed on a 

 background half black and half white and the black half covered with black cloth, 

 the larvse remain on the dark side of the dish. Those that attempt to pass to the 

 light side turn back at once. If the larvse are hungry this reaction does not take 

 place. It is also noteworthy that when a school of young larvse is seen with the 

 male in direct sunlight, the school if undisturbed and in open water moves usually 

 in the shadow of the male. It is probably this reaction which helps to keep the 

 schools of young larvse together. Such a school is a dense black mass, so that a 

 larva passing beyond the borders of this mass tends to react, as does a larva pass- 

 ing beyond the border of a dense shadow — the larva tends to turn back into the 

 black mass of its fellows. 



Larvse of 12 to 20 millimetres show no evidence of such reaction; they may 

 be said to show no fear. If a stick be thrust into such a school and moved about, 

 the larvse make no effort to escape, but move toward the stick quite as often as from 

 it. They are often seen to be buffeted about by the fins of the male as he moves 

 above the school, but they show no reaction to such stimulus. When the fright- 

 ened male rushes away from the school, often with great violence, the larvse do not 

 scatter and hide, but after a little begin to circle in the manner already described. 



