OUTLINE OF LABORATORY WORK IN THE STUDY OF THE VENATION 

 OF THE WINGS OF INSECTS* 



IXTRODUCTIOX 



In form an insect's wing is a large, membranous app2ndage, which is 

 thickened along certain lines. These thickened lines are termsd the veins 

 or nerves of the wing; and their arrangement is described as the venation 

 or neuration of the wings. 



It has been found that the venation of the wings of closely allied insects 

 is very similar, and that great differences in this respect exist between 

 insects remotel}' connected. Hence, the wings afford excellent characters 

 for use in the classification of insects. In fact, as slight differences in 

 \'enation are easily observ^ed, the wings being spread out like an open page, 

 these differences are probably the most available characteristics of winged 

 insects for taxonomic work. It is important, therefore, that the student 

 of entomology should learn early in his course the more important facts 

 regarding this subject. 



A careful study of the wings of many insects has shown that the fuida- 

 mental type of venation is the same in all of the orders of winged insects. 

 But this fact is evident only when the more primitive or generalized mem- 

 bers of different orders are compared with each other. In most of the 

 orders of insects the greater number of species have become so modified or 

 specialized as regards the structure of their wings that it is difficult at first 

 to trace out the primitive type. 



Note. — The student should have a clear idea of the significance of the terms genera- 

 lized and specialized, which are now much used in biology. Generalized indicates a 

 primitive condition, a nearness to ancestral forms. Thus, the most generalized member 

 of a group (as a family or an order) is that memb2r which most clearly resembles the 

 ancient progenitor of that group. Specialized, on the other hand, indicates remoteness 

 from the primitive type, an adaptation to more special conditions of existence. Thus, 

 the most specialized member of a group is the one that departs most widely from the 

 ancient progenitor of that grouj). 



These terms are used in a com"parative sense; thus, a highly specialized form may 

 be regarded as generalized when compared with forms that are still more highly specia- 

 lized. 



This agreement in the important features of the venation of the wings of 

 the generalized members of the different orders of insects is still more 

 evident when the wings of nymphs and pupx are studied. It has been 

 demonstrated that in the development of the wings of generalized insects the 

 longitudinal wing-veins are formed about preexisting tracheae. In the 

 course of the development of the wing, these tracheae grow out into the 

 wing-bvid, and later the wing-veins are formed about them. 



*The material for this outline has been drawn largely from The Elements of Insect 

 Anatomy, by John Henry Comstock and Vernon L. Kellogg, published by the Com- 

 stock Publishing Company, Ithaca, N. Y. 



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