INTRODUCTION 



17 



and Kellogg is based on the theory that many veined wings antedated those 

 with few veins and corresponds with the idea of eleven primitive veins. 



The placing of Orthoptera lowest by Folsom and Sanderson follows those 

 who do not think that wings arose as tracheal gills or in aquatic insects. 



The arrangement of the four largest and most recent groups, Coleoptera, 

 Diptera, Hymenoptera and Lepidoptera is given differently by each author 

 with no very evident reason. 



Neopterd 



Elytro^tera. 



KorrodenticL 

 SubuU 



Figure 13. Diagram of tlie genetic relationships of the groups of insects and 

 the three types of venation. 



ORDERS OF INSECTS. 



Coleoptera: spiracles and dorsal abdominal segments not visible from be- 

 neath. 



Lepidoptera: densely covered with scales. 



Diptera: hind wings club-like, or if wingless, thorax separated by constric- 

 tions from head and from abdomen, and without opposable jaws. 



Hymenoptera: wings hooking together and front wings very narrow near 

 the base, or if wingless, greatly constricted at base of abdomen. 



Hemiptera: mouthparts tubular, or with long threadlike lancets, or very un- 

 symmetrical, or wanting. 



Orthoptera: front wings leathery, or if wingless, either front or hind legs 

 are much enlarged, or body is flattened, or thorax is very slender cylindrical. 



Corrodentia: ant-like or louse-like. 



Neuroptera. Odonata: wings notched near the middle of the front edge. Ap- 

 tera: wingless and legs shorter than body. Ephemerida: with three tails. 



