518 HEMIPTERA. 



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

 coon, and changes into an inactive pupa. 



Apterous individuals, especially i'emales, sometimes occur, 

 especially in the aquatic Hydrometra, Velia and Limnobates, 

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

 absent. 



The embiyological development of such Hemiptera as 'have 

 been observed (H>/dronietra, Cvrixa, Aphidce, Coccidce, 

 PC d i cu I i n a and H a 1 1 op li a g a ) corresponds very closely with 

 that of certain Neuroptcra (L i b<- 1? /i}f d ce and lie m c ro b i d ce . 



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

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

 containing the aquatic genera, Velia, Xepa, Belostonm and 

 Notonecta, and Avhich first appeared in the Jurassic formation. 



Latreille divided the Hemiptera into the Heteroptcra and 

 Homoptera. The latter are the higher in rank, as the body is 

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

 in the Aphidce, 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 spepies are smaller than in the Heteroptera, 

 and are all terrestrial. The Hetcropterous 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), and 

 several families arc 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 as and 

 ITnmoptera 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 

 bod}', and the head is held vertically, where in most Heterop- 

 tera it is horizontal and flattened. 



