118 Wisconsin Academy of Sciences, Arts, and Letters. 
both, eggs and young were present only during tbe warm 
weather, being most abundant early in summer. 
Tbe question of Entocy there being a parasite or a commensal 
is one that could not be answered from its habitat alone. Liv¬ 
ing in tbe branchial chamber and on the branchiae and bran¬ 
chial filaments of the crayfish it might have no further connec¬ 
tion with its host than to obtain a sheltered abode. The num¬ 
ber of other animals found living in the branchial cham¬ 
ber could supply it with sufficient food, but these, being prin¬ 
cipally nematodes and rotifers, would leave traces of their iden¬ 
tity in the stomach contents. An examination of all my speci¬ 
mens showed that in most, of them the stomach was either empty 
or filled with a nearly homogeneous, mass. While the mouth 
parts of Entocy there are not modified for a parasitic life, I be¬ 
lieve that its food consists of the blood circulating in the bran¬ 
chiae of the host. 
The method of infection appears difficult of elucidation. At 
no stage in its lifeffiistory has Entocythere the power of swim¬ 
ming, so that it is unable to go through the water from one host 
to another. During the copulation of the crayfish it, could eas¬ 
ily pass from one individual to another, or could reach the 
young as long as they remained attached to the swimmers of the 
mother. The latter view does not seem probable as I never 
found any of the very young crayfish infected, always finding 
the parasites most abundant in the largest individuals. 
At one time I obtained from the same locality near Madison, 
over thirty crayfish which were all placed in a; large sink. Fif¬ 
teen of them, killed within two days, were found to be well in¬ 
fected, more than half containing parasites. The remainder 
of the loti were kept together for more than four weeks, and 
when finally killed, every one was found infected; the number 
of parasites being greater than in any other crayfish I ever ex¬ 
amined. It seems improbable that the first lot of crayfish 
were any less infected than those not selected, but more likely 
that had they also been examined when first obtained, nearly 
half of them would also have been free from) parasites. I do 
not see why in taking half of the lot I should have selected those 
in which the per cent of infected specimens was smallest, or in 
