32 THE UNIVERSITY SCIENCE BULLETIN. 
the “Larval water mites of aquatic animals” in the American 
Monthly Microscopical Journal, Vol. XXII, pp. 323-324, and 
a key for determining Hydrachnids is to be found in “Fresh 
Water Biology,” by Ward & Whipple. 
Besides the mites an undetermined internal parasite has 
been discovered in the body cavities of Notonectids and Cor- 
ixids. These the writer has frequently seen, as well as spher- 
ical spore cysts of a gregarine to be found in the body cavity of 
Corixids. 
Parasitism by Hymenoptera has been observed in a very 
few cases. These have been egg parasites and belong to the 
following families: Chalcidide#, Proctrotrypide and Myma- 
ride. In the first family we have the frequently mentioned 
Prestwichia aquatica Lubbock, which has been reared from 
the eggs of Notonecta and Ranatra as well as those of beetles. 
In the Proctrotrypide there are recorded two species at 
least. Limnodytes gerriphagus March and L. setosus De Ste- 
fani Perez, both of which parasitize Gerris eggs. Matheson 
and Crosby reared the former species from the eggs of Gerris 
remigis in June, at Ithaca, New York, and also a Mymarid, 
Caraphractus cinctus Walker from eggs which they found 
inserted in the tissues of plants on December 7. On December 
19 some young back-swimmers were swimming about and also 
some of the little wasps had emerged and were actively swim- 
ming in the water. As many as four parasites emerged 
through one opening in one egg. This parasite uses its wings 
in propelling itself through the water. 
The fact that these notes were made upon eggs inserted in 
plant tissues and taken in the winter time, limits the host 
species to N. trrorata or one of the Buenoz, and throws new 
light upon the wintering of back-swimmers. The species 
above mentioned are known to winter as adults, though the 
presence of eggs is not impossible, for one of the Kuropean 
Notonectids is known to pass the winter months in the egg 
stage. The field of study along these lines would well repay 
investigation. Brocher has also recorded a hymenopterous 
parasite from the eggs of Hydrometra. Doubtless there are 
many other parasites to be found by careful rearing. 
No internal parasites of either nymphs or adults of any of 
the water bugs have been reported in the literature so far as 
the writer knows. 
