510 INVERTEBRATE MORPHOLOGY. 



similar to the adults and the metamorphosis is gradual, 

 though the tendency towards the development of a distinct 

 pupal stage is shown by the fact that the last larval stage 

 takes no nourishment. The genus Phlceotkrips is character- 

 ized by the last abdominal segment being tubular in form, 

 while Tlirips possesses in the female forms an ovipositor com- 

 posed of four valvelike pieces. 



8. Order Rhynchota. 



The .members of this order are divisible into two groups, 

 the Heteroptera and ffomoptera, according to the character of 

 the anterior wings. In the Heteroptera, which includes the 

 majority of forms popularly known as Bugs, the basal partions 

 of the anterior wings are chitiuous, while the tips are mem- 

 branous, the posterior wings being entirely membranous. A 

 typical member of this group is the common Squash-bug 

 (Anasa, Fig. 238, A), and other examples are the Water-boat- 

 man (Notonecta), the large Water-scorpion (Belostoma), and the 

 slender Water-scorpion (JKanatra), all of which are of frequent 

 occurrence in ponds, swimming powerfully beneath the water 

 by means of the flattened posterior legs which serve as oars, 

 the anterior pair being directed forwards and serving for 

 grasping the prey. The Water- measurer or Water-spider 

 (Hydrometra) is also veiy common in ponds, darting about 

 upon the surface in search of prey, a habit which also char- 

 acterizes the genus Halobates, which lives upon the surface of 

 the ocean and is found many miles from land. Some mem- 

 bers of the group are entirely destitute of wings, as for ex- 

 ample the Bedbug (Gimex) and the Louse (Pediculuti). 



In the Homoptera the wings are both membranous, the 

 anterior pair being larger than the posterior, and, as in the 

 other group, are sometimes wanting. The Cicada is a member 

 of this group, as are also the Aphidse, or Plant-lice (Fig. 230), 

 so frequent in green-houses and upon various uncultivated 

 plants whose juices they suck, a habit also shared by the 

 nearly -allied Coccidse, including the scale-insects (Aspidiotus) 

 and the Mealy-bugs (Dactylopius), both of frequent occurrence 

 on cultivated plants, the former sometimes doing no little 



