56 CLASSIFICATION OF INSECTS. 



and study ; and even then one is liable to be deceived 

 by appearances, and may expect to make serious errors 

 in spite of the most elaborate precautions. 



The general acquisition of wings, through outgrowths 

 from the two hinder segments of the thorax, first as 

 mere spurs, then as articulated pads in the pupae, has 

 naturally led to the conclusion that these organs were 

 also gradually acquired by some similar gradations in 

 ancestral forms. Some entomologists hold that they 

 may have been modified legs,^ but many entomolo- 

 gists regard them as having arisen from organs similar 

 to those now found upon the abdomen of the larvae of 

 May-flies. These larvae have gills for aerating the blood 

 growing out from the rings on the upper side of the 

 abdomen, and often some of these are modified into 

 protective coverings. Thus the branchiae on some 

 rings may be transformed into articulated scales, which 

 resemble the wing pads of the pupae, and these appear 

 to explain the origin of the larval outgrowths and the 

 true wings, which appear upon the meso- and meta- 

 thorax.^ Fritz Mtiller and Packard, after careful and 

 independent investigation, have both rejected this 

 hypothesis. They confined themselves to closer com- 

 parisons of the facts afforded by the development of 

 wings in pupae, and recognized the difficulties attach- 



1 Dr. Hagen, "On Some Insect Deformities," Mem. Mus. 

 Comp. ZooL, Vol. II., No. 9, p. 22, quotes, in support of this 

 opinion, an extraordinary case, in which the fore pair of wings 

 were replaced by a pair of articulated legs in Prionus coi-iarius. 



2 Miall and Denny {St7-uctiire and Life- Hi story of Cockroach, 

 p. 63, Lovell, Reeve & Co., London) give an excellent account 

 of this theory with explanatory figures. 



