CHAPTER VI 

 THE STEPS IN THE SPECIALIZATION OF WINGS 



In order to make use in taxonomic work of the characters presented by 

 the wings of insects, it is necessary to gain a clear idea of what are the more 

 generalized features of these wings and of the various ways in which the 

 primitive type of insect wing has been modified. With this data in hand 

 much information is available, that will be of use in determining the 

 relationships of the subdivision of the class Insecta. 



The making of a genealogical tree does not fall within the scope of this 

 book. The writer fully appreciates that a natural classification of insects 

 cannot be based on the study of a single set of organs. But there can be no 

 doubt that the wings of insects present characters that will be of great value 

 in the working out of such a classification. 



While no attempt to construct a genealogical tree is to be made here, it 

 is desirable that the data that can be obtained by a study of the wings 

 should be presented in such a way that it shall be available for correlation 

 with the data to be derived from the study of other parts. For this reason 

 there is given in this chapter a brief discussion of the methods of specializa- 

 tion of wings and, at the close of the chapter, an analytical table of the 

 orders of insects based on the different methods of specialization of these 

 organs characteristic of the different orders. 



The sequence in which the orders of insects are discussed in the following 

 chapters has been determined by this table. This sequence, like all linear 

 arrangements of groups of organisms, is more or less arbitrary. Thus while 

 there is an effort to place first the more generalized orders and later those 

 that are more specialized, the putting together of orders exhibiting the 

 same type of specialization results in some cases in the placing of compara- 

 tively generalized forms after those that are obviously more highly spec- 

 ialized. The position of the Plecoptera is an illustration of this. The 

 insects of this order are evidently more generalized than, for example, the 

 Neuroptera or the Odonata, which are placed earlier in the linear 

 series. 



The comparatively high position assigned to the Plecoptera is, however, 

 only apparent. A reference to the table will show that the orders of insects 

 are grouped in two series, "A" and "AA". Under "A" are placed those 

 orders in which the wings are specialized by addition in the preanal area 

 and under "AA" those orders in which the wings are specialized by reduc- 

 tion in the preanal area. Each of these series includes some quite general- 

 ized insects and others that are highly specialized. The completion of the 

 discussion of the first series before taking up the second series results in the 



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