518 HEMIPTERA. 



Coccus, which, as in the higher suborders, spins a silken co- 

 coon, and changes into an inactive pupa. 



Apterous individuals, especially females, sometimes occur, 

 especially in the aquatic Hydrometra, Velia and Limnobates, 

 and in many other genera the hind pair of wings are often 

 absent. 



The embryological development of such Ilemiptera as have 

 been observed ( Hydro met m, Corixa, Aphid IK, Cocci don, 

 J'edicn I ! n <t and Mallophagoi) corresponds very closely with 

 that of certain Neuroptera (Li In']] iilid> and Hemerolj idv . 



There are about 12,000 species living and fossil. Some 

 species are of great size, especially the Hydroeores, a division 

 containing the aquatic genera, Velia, Nepa, Belostoma and 

 Notonecta, and which first appeared in the Jurassic formation. 



Latreille divided the Ilemiptera into the Heteroptera and 

 llomoptera. The latter are the higher in rank, as the bod}' is 

 more cephalized, the parts of the body more specialized, and 

 in the Aphidd'. which top the series, we have a greater sex- 

 ual differentiation, the females being both sexual and asexual, 

 the latter by a budding process, and without the interposition 

 of the male producing immense numbers of young, which feed 

 in colonies. The species are smaller than in the Heteroptera, 

 and are all terrestrial. The Heteropterous Hemiptera, on the 

 other hand, are larger, the body is less compactly put together, 

 the abdomen and thorax are elongated, the head is small com- 

 pared with the rest of the body, and the species are large, 

 some of great size (a sign of degradation among insects), :md 

 several families are aquatic, indicating a lower grade of devel- 

 opment, while representatives of these were the first of the 

 suborder to appear in geological times. Their affinities are 

 with the Orthoptera and Neuroptera, while the Aphid ami 

 Homoptera generally, on the other hand, whose bodies are 

 more cylindrical, ally themselves with the first and higher se- 

 ries of suborders. 



In the Homopterous Hemiptera the fore pair of wings are 

 generally transparent and usually net-veined, lying with the 

 hind pair, which are considerably smaller, roof-like upon the 

 body, and the head is held vertically, where in most Heterop- 

 tera it is horizontal and flattened. 



