ENTOMOLOGY 



Needham.) The former, or outward, kind of coalescence is common 



in most orders of insects; the latter, or inward, kind is especially 



prevalent in Diptera. 



Specialization by addition occurs by a multiplication of the branches 



of the principal veins, or by the development of secondary longitudinal 



veins between these branches. 



Corns tock and Needham have succeeded in homologizing practically 



all the types of neuration, 

 including such perplexing 

 types as those of Ephemerida 

 (Fig. 72), Odonata (Fig. 21, 

 B) and Hymenoptera (Fig. 

 73), and have established a 



uniform terminology of the 

 wing veins. The system built 

 up during some twenty-five 

 years by Comstock and his f ol- 



PIG. 72 .-WingsofaMayfly. Lettering as before, lowers is embodied in his great 



volume, The Wings of Insects. 



A student of the subject of venation should consult the many articles 

 by Tillyard, a keen investigator, whose point of view is in some respects 

 different from that of Gomstock and Needham. He holds, for example, 

 that the primitive type of wing had many veins instead of few, and 

 that the evolutionary tendency has been, generally speaking, toward a 

 reduction in the number of veins. 



FIG. 73. A typical hymenopterous wing. Lettering as before. 



Folding of Wing. In some beetles (as Chrysobothris) the wings are 

 no larger than the elytra and are not folded; in others the wings exceed 

 the elytra in size, and when not in use are folded under the elytra in 

 ways that are simple but efficient, as described by Kolbe and by Tower. 

 To be understood, the process of folding should be observed in the 

 living insect. As described by Tower for the Colorado potato beetle, 



