88 NATURAL HISTORY OF AMIA CALVA LINNiEUS. 



diameter and near the edge of the enclosure." The movements of the individuals 

 in this swarm were back and forth like trapped Paramcecia, each turning and 

 returning within the swarm upon passing its border. Many individuals fre- 

 quently move in the same direction at the same time. Occasional shifting of the 

 swarm is produced by an individual or group of individuals moving farther than 

 usual beyond the boundary before beginning to return. There is thus produced a 

 slight pseudopod-like lobe to the swarm. This lasts long enough to permit other 

 individuals of the swarm to enter it, until finally the centre of density of the swarm 

 is shifted and the swarm has moved. When the swarm had moved thus about a 

 foot it became centred about a bunch of five or six erect, loosely aggregated grass- 

 stems and there began then a definite rotation of the swarm in a direction opposite 

 the hands of a watch. The individuals moved at this time at the rate of about 1.5 

 centimetres per second. After six and one-half minutes the movements became 

 again indefinite and the swarm contracted. Shortly it began to rotate in the 

 opposite direction and continued this for four minutes. It then became again con- 

 tracted and the movements irregular. Fifteen minutes later it was again circling 

 counter-clockwise, and four minutes later in the opposite direction. Five minutes 

 later the swarm again moved to a distance of a foot and then became stationary. 

 Sometimes the swarm remains quiet for three-quarters of an hour. "This quiet 

 state is one in which the individuals are moving indefinitely back and forth, but 

 very slowly, and more slowly at the centre than toward the edge. Indeed they 

 usually stop or nearly stop at the centre. There is thus produced a swarm dense 

 at the centre and loose at the edge, in this case 15 to 18 centimetres in diameter 

 and with its central five centimetres very dense. In the one instance in which I 

 studied the larvae in the nest at night they were found in a stationary swarm, nearer 

 the bottom than is usual by day. They came a little nearer the surface under the 

 influence of the light. 



H. The larvae begin to feed while still in the nests. In bright sunlight one 

 may see numerous small Crustacea among the rootlets of the bottom. The larvae 

 may be seen springing at these, and their success is attested by the strings of fecal 

 matter often seen protruding from their anal openings. Larvae 11 millimetres long 

 when taken from the nest were found to have the stomach well filled with small 

 crustaceans, chiefly ostracods. 



Larvae which have reached the length of 12 millimetres are then black, the 

 yolk-sac is two-thirds absorbed, the adhesive organ is no longer used, they are 

 swimming by means of intermittent vibratory movements of pectoral and caudal 

 in swarms which move progressively but irregularly, and they are feeding. They 



