130 AN INTRODUCTION TO ENTOMOLOGY. 



males of the Coccidae present a remarkable exception in the nature 

 of their transformations, the metamorphosis being a complete one. 



This order includes three well-marked groups ; these are ranked 

 as sub-orders, and are distinguished as follows : 



TABLE OF SUB-ORDERS OF HEMIPTERA. 



A. Wingless Hemiptera, parasitic upon Man and other Mammals, with a fleshy 

 unjointed rostrum.* I. PARASITA. 



AA. Hemiptera with or without wings, but with a jointed rostrum. 



B. Wings of the same thickness throughout, and usually sloping at the sides 

 of the body; rostrum arising from the hinder part of the lower side of 

 the head ; head without neck, and so closely applied to the prothorax 

 that the first pair of coxae articulate with the cheeks. II. HOMOPTERA. 

 BB. First pair of wings thickened at the base, and with thinner extremities, 

 which overlap on the back ; rostrum arising from the front part of the 

 head ; head (except in Corisidce and Notonectidce) with a more or less dis- 

 tinct neck, so that the cheeks and the first pair of coxae do not touch 

 each other. III. HETEROPTERA. 



Sub-Order I. PARASITICA. 



The Parasltica includes certain parasites of Man and other Mam- 

 mals, commonly known as lice. All the species which have been 

 found in the United States belong to a single family, the Pedicu- 

 lidce. We will not, therefore, enter into a discussion of the charac- 

 ters of the sub-order, but pass directly to a study of this family. 



Family I. 



(Lice.} 



The lice are very small, wingless insects, which live on the skin of 

 Mammalia, and suck their blood. The mouth is furnished with a 

 fleshy, unjointed proboscis, which can be withdrawn into the head, 

 or extended to a considerable length. Within this proboscis are 

 two protrusible knife-like stylets ; and at its base, when extended, 

 there is a wreath of re-curved hooks. These hooks serve to anchor 

 firmly the proboscis when inserted in the skin of the infested ani- 

 mal. The eyes are two in number, small and simple. The antennae 

 have five segments. The legs are joined to the outer margin of the 



* This is true of all forms that have been found in the United States. But in the 

 genus Polyctenus the rostrum is three-jointed. Two species of this genus are known ; 

 these infest bats ; one in the West Indies, the other in China. 



\ Pediculus, a louse. 



