Horizontal Distribution — Swarms. 
373 
Two similar swarms of the same species were seen in 1896 on 
October 3rd, and on November 3rd; both days w r hen the lake 
was perfectly calm. On the first occasion there was a fog on 
the water; on the second occasion the sky was clear. 
These swarms were nearer the shore and were much more exten¬ 
sive. On the first occasion the Daphnias occurred in patches of 
irregular extent and shape—perhaps 10 meters by 50 meters, 
and these patches extended in a long belt parallel to the shore. 
The surface water was crowded by the Daphnias, and an im¬ 
mense number of perch were feeding upon them. The swarm 
was watched for more than an hour, during which the fog passed 
away, and the water could be seen disturbed by the perch along 
the shore as far as the eye could reach as one was standing in 
a boat. After a time a light breeze sprang up and, of course, 
prevented further observation. On this occasion the number 
was determined to be 1,170,000 per cu. m. in the densest part 
of the swarm. On November 3rd a similar swarm was seen, 
and water was again dipped up from the denser part of the 
swarm. The Crustacea were crowded into an extremely thin 
layer, not more than 2-3 cm. thick. The surface water only 
was allowed to fall into the vessel and the number determined 
in 6 catches made by straining 10 liters of water, was from 
800,000 to 1,492,000 Daphnias per cubic meter, about 99 per 
cent, adult. In addition there were present about 1,000 Cyclops 
per cubic meter, but nothing else was found. On this occasion 
one ephippial female was present, the only one that I have ever 
seen in this species; the ephippium was fairly developed, but 
no eggs had been deposited in it. No males were in these swarms. 
The highest number is found nearly ten times the maximum 
number of this species per cubic meter, as derived from the 
three-meter hauls. It is also nearly fifty per cent, more than 
the maximum catch of this species as obtained from a depth of 
18 meters, and nearly five times as great as the average for 
November 1-15. On November 3d, catches were made below 
the swarm from 0.3m. to 3.3m. The average of two gave per 
cubic meter: 
Diaptomus . 4,900 
Cyclops . 26,600 
D. hyalina . 18,200 
C'hydorus ... 15,700 
