io6 Hemiptera-Homoptera. 



ticulated sheath (labium). The maxillary and labial palpi are obsolete. 

 In some species the mouth-parts are almost as long as the body. 



The larviE resemble the adult insects but, at first, want wings. Rudi- 

 ments of these begin to appear after the first moult, and with each succes- 

 sive moult they are further developed. 



The pupa; are active and differ mainly from the larvie in having larger 

 wing-pads. A remarkable exception occurs in the case of the male Coc- 

 cus, the larvae of which spins a silken cocoon, and changes into an inac- 

 tive pupa. (I, 5'7)- 



All the insects of this sub-order are terrestrial, and live upon vegetable 

 j uices. Many are remarkable for covering themselves with excretions from 

 their bodies. The females are often furnished with a complicated oviposi- 

 tor. 



Examples of the three more important families will be noticed. 



Aphid.'E {Plant-lice).* 



The small green plant lice, so common on plants, 

 both in the fields and in the house, are familiar exam- 

 ples of this family, and will serve as illustrations of 

 the typical form of its members. 



Plant-lice are found on nearly all parts of plants, — the 

 roots, stems, buds, leaves, and flowers. They derive 

 their nourishment by sucking the juices of the plants, 

 and are sometimes very injurious, as their powers of 

 reproduction are immense, (i, 519; 14, II., 437; 8, 

 III., 281— 412; 8, VI., 523; 2,232). 



Many of our common species belong to the genus 

 Aphis, which may be recognized by the long honey- 

 tubes, the presence of the fourth or stigmal vein of 

 the anterior wings, and the seventh, or last, joint of 

 the antenna being longer than the sixth joint. 



The mode of reproduction in this group has been 

 carefully studied, and presents some striking peculiar- 



* See paper entitled " On the genera of Aphid.X' found in the United States," by I^enj. 

 D. Waish, JO, I., 394. 



