INTRODUCTION 3 



characters recorded in the following table will serve not only to 

 separate these orders from each other, but will also serve to 

 separate them from all the other orders of insects: — 



a. Legs normal in form, fitted for walking or swimming, never scan- 



sorial or with tibia and tarsus and claw of each leg combined to 



form an opposed thumb and finger for clinging to hairs; labium 



modified into a distinct always exposed sucking tube, if wanting, 



thorax with a single pair of wings or the tarsi with a single claw 



or legs wanting. 



b. Tarsi with the distal segment bladder-like or hoof -like in form; 



wings long, narrow, subequal in size, margins parallel and fringed 



with setae as long as the width of wing; labium a conical tube 



enclosing one mandible and two maxillae; maxillae and labium 



provided with palpi; clypeus asymmetrical in the adult; legs and 



mouth-parts always present Piiysopoda. 



bb. Tarsi with the distal segment never bladder-like or hoof-like in 

 form; wings triangular or subtriangular in outline, one of the 

 wings of each side usually larger than the other, never with 

 margins parallel and fringed with long setae; labium a segmented 

 tube enclosing bristle-like mandibles and maxillae; maxillae and 

 labium never provided with palpi; clypeus always symmetrical; 



legs and mouth-parts sometimes wanting Hemipteba. 



aa. Legs abnormal in form, never fitted for walking or sv/imming, 

 always scansorial or with tibia and tarsus and claw of each leg 

 combined to form an opposed thumb and finger for clinging to 

 hairs; labium modified into a sucking tube that is usually retracted 



and concealed; wings always wanting and legs always present 



Anoplura. 



The Anoplura or lice are generally included as a suborder 

 of Hemiptera under the name of Parasitica. The evidence that 

 they are degraded Hemiptera is not very conclusive. The form of 

 their mouth-parts, a closed sucking tube without mandibles or 

 maxillae, is very different from that of the species of this order. 

 The order Hemiptera can be characterized more definitely and the 

 Anoplura more easily differentiated from the Hemiptera if it is 

 considered as a distinct order. 



The order Hemiptera is usuallj" divided into three suborders, 

 Hetcroptera, Homoptera, and Parasitica. The last of these has 

 been recognized as a distinct order as already indicated. The 

 texture of the wings, the shape and position of the head, the point 

 of attachment and structure of the labium or rostrum, the form of 

 the tarsi, and the form, size, and presence of the antennae are 

 the characteristics generally used to distinguish the suborders 

 Heteroptera and Homoptera. The difference in the form of the 



