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SOI 111 INDIAN tNSECTS, ET< - 



|< HAP. i. 



da) occasional traces are found of this primitive tendency, as 

 maj be seen in figure to, which shows an immature nymph of a 

 Sinhalese Termite. The fact that all known adult modern insects 

 have concurred in the nondevelopment of the prothoracic wings 

 seems to lend some support to the idea of a monophyletic desi enl 

 of the 1 lexapods. 



The wings are composed of two layers, each a thin membrane 

 oi chitinous material, between which there may be trachea;. Each 

 layer is traversed by horny ribs or nervures, often loosely but 

 incorrectly called veins, which serve as a framework for the support 

 of the wing. The size, shape, number and interconnections of 

 these nervures are extremelj various although usually fairly con- 

 stant in general pattern in each group of insects and they are thus 

 ol great importance for purposes of classification for which they 

 have been used especially in the case of the Lepidoptera and 



i Diagram of a enci dized Insect- wing. I Mtei Snodgrass, U.S.A. 



Techn. Bull. No. 18.) 



i.i. Sc, Sub-costa, typically dividing into two branches ^> 1 and Sc2. 

 K.Radius dividing dichotomously into five branches Rl RS, the anterior fork 

 of the In i branch remaining single. M. Media, dividing into four branches, 

 Ml — M4. Cu, Cubitus, which i- again two-branched, Cul, C'u_'. The remain- 

 ing single free veins al base of wing are Anals, IA, 2A, etc. ["he cro 



I and Sc, neai base, i i 1 • Humeral Cross- vein ; that between R and 



i Radi dial I ross-vein : that between M 



Medio-cubital Cross-vein; that between M2 and M3 

 is the Median Cross vein, rhe ireas enclosed b; cro veins are called cells. 



Diptera. As the wings in all inse< ts are presumably modifications 

 ol one original pattern, manj attempts have been made to prepare 

 and name one general type of neuration applicable to all modern 

 insects, but no system of thi> kind has hitherto met with general 

 acceptance. An example of a generalized type of insect neuration 

 is shown in figure ii but in practice it is often extremelj difficult to 



