The origin and development of the wings of Coleopterii. 549 



and develop in the same way for most of the larval period, that they 

 are not the fore wings inhibited at an early stage, but are divergent 

 structures specialized for a new function. This view is based upon 

 the more widely separated lamellae of the elytron, the presence of 

 more chitin and the existence of a secondary internal cavity connecting 

 with the body cavity. 



My observations convince me that the elytra are homologous to 

 the fore wings of other insects for the following reasons: 1) They 

 arise in exactly the same way as do the wings of all insects, and 

 follow much the same course of development during the larval and 

 pupal periods ; 2) they are supplied with temporary and permanent 

 tracheal systems which are always lodged in a definitely located system 

 of veins, as in the hind wings and in the wings of other insects ; they 

 behave during the prepupal and pupal stages as do the wings of other 

 insects. To regard the elytra as ''divergent structures specialized for 

 a particular function" (KrüC4er 1899) is impossible, since it could not 

 reasonably be expected that a "divergent structure" could be found 

 which was not a wing, yet occupied the same position, and had the 

 same function, course of development exactly like the wings of other 

 insects, and a structure venation and tracheation that was in every 

 way characteristic of insect wings. 



The contention of Krüger (1899) that the elytra are not wings 

 is based upon structures that appear late in development, and no 

 wright has been given to the fact that the elytra and wings arise in 

 the same way and develop alike for most of their period of develop- 

 ment. Most of this authors' observations were based upon material 

 that had been treated with nitric acid to soften the chitin. This process 

 is in my experience absolutely untrustworthy. 



9. The Prepupal Stage and Pupation. 



In the preceding sections I have shown how the wings originate, 

 grow, and finally get outside of the body and become external struc- 

 tures; in this section I shall trace the growth and development of 

 the wings during the prepupal period. In the prepupal stage, which 

 rarely lasts more than a few days, the wing grows with great rapidity, 

 changes in form, and comes always to assume a definite position. 

 It is interesting to follow closely some of these changes and to deter- 

 mine their causes. 



After the larva ceases feeding it empties the alimentary canal of 

 most of the food and seeks a place in which to pupate. During this 



