com SI DM 141 



the groups are aquatic, a number terrestrial, and some 

 arboreal. The aquatic forms are derived from the terres- 

 trial. Most of them are obliged to come to the surface of 

 the water to secure air at various intervals and this shows 

 that they are modified from terrestrial forms. The aquatic 

 forms pass the larval stage in the aquatic life but in most of 

 the aquatic families the adults are also aquatic, though they 

 may issue from the water and fly readily out of water. The 

 eggs of aquatic forms are deposited on aquatic plants dis- 

 tributed in the water and only in a few cases do they show 

 marked peculiarities in the matter of egg deposition. In 

 one of our common species, the smaller water bug (Zaitha 

 fluminea), the eggs are deposited on the back of the male 



c b a 



Fig. 94. — Water bugs: a, water boatman, Corisa harrisii; b, Notonecta 



irrorata; c, Notonecta undulata. Enlarged X 1.42. (Photo by C. J. Drake.) 



by the female in a rather large mass, the eggs being set on 

 end attached to the wing covers and are carried in this way 

 for some time until they hatch. 



Of the terrestrial forms there are a considerable number of 

 families. Some important species, chinch bug, squash bug, 

 etc. The effect of the chinch bug on cereal crops is very 

 damaging. 



Water Boatmen {Corisidcp). — The water boatmen are small 

 species. Their legs are modified for swimming, the hind 

 ones being long, wide, and oar-like, having a series of cilia 

 which aid much in swimming. The species are found in large 

 numbers in ponds and streams, occasionally they fly in large 

 swarms. Spring is the usual time when they are seen flying 



