204 ENTOMOLOGICAL NEWS [May, 'l/ 



while the third pair is used only in steering, both tibia and 

 tarsus lying on the surface for this purpose. The wings, when 

 present, are serviceable, the European forms being recorded 

 as using them in night flights, not observed with our species. 



It is said that when closely pursued Gerris dives to escape 

 and swims under water, but I have never been able to induce 

 or force any of those I have seen to perform for me. 



Gerris remigis is parasitized by a bright red water mite, 

 which attacks it in all stages of development. I have found 

 in midsummer an individual with head completely covered with 

 these larval mites, excepting the eyes and beak ; a winged speci- 

 men had the thorax invaded. In September a young nymph 

 was taken similarly infested. Matheson and Crosby^ observed 

 the minute Proctotrypid, Limnodytes gerriphagus, also known 

 in Europe as a parasite of gerrid eggs, ovipositing on those of 

 remigis, one to each egg. 



The external anatomy of Gerris remigis is fairly known, but 

 so- far no one has worked out the internal anatomy and physi- 

 ology of the species. Dufour^ investigated the anatomy of its 

 European congener, Gerris najas de Geer (canalium Dufour). 

 He studied the digestive tract, the hepatic and the reproductive 

 systems, and in pi. V, Figs. 59-64, he illustrated certain ana- 

 tomical details and also the digestive tract. He states that "the 

 stigmata of Gerris are of microscopic size and very difficult to 

 detect because of the lustrous silky pile which covers them. 

 There are six pairs, all near the outer edge of the venter, out- 

 side of darker lines." He also says the trachea are tubular 

 and elastic and of capillary fineness. Dufour also remarks 

 that it has an alcalescent odor and quotes De Geer as calling it 

 buggy. I myself have not noted this in remigis. Bergroth* 

 describes a perforated median tubercle in the metasternum, 

 which he calls "omphalium," and queries if it be the unpaired 



-1912. Ann. Ent. Soc. Am. v: 67. Aquatic Hymenoptera in America. 

 Robert Matheson and C. R. Crosby. 



3 1833. Recherches Anatomiques et Physiologiques sur les Hemi- 

 pteres. Memoires de Savans Etrangers, pp. 197, 346, 371, 400. 



* 1902. On the Thorax of the Gerridae, Ent. Mo. Mag. (2), xiii, 

 258-260. 



