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 : Chalcididse, Proctrotrypid^e and Myma- 

 ridse. In the first family we have the frequently mentioned 

 Prestiuichia aquatica Lubbock, which has been reared from 

 the eggs of Notonecta and Ranatra as well as those of beetles. 



In the Proctrotrypidae 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, 

 Cai'aphractus 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. irrorata or one of the Buenose, 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 European 

 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. 



