196 



AN INTRODUCTION TO ENTOMOLOGY 



portions of tne invagination (Fig. 216, c). During the fourth 

 stadium, the evaginated part of the histoblast becomes greatly- 

 extended (Fig. 216, d). 

 It is this evaginated 

 portion of the histo- 

 blast that later be- 

 comes the wing. Dur- 

 ing the fifth stadium 

 the wing-bud attains 

 the form shown in 

 Figure 216, e, which 

 represents it dissected 

 out of the wing-pocket 

 At the close of the last 

 larval stadium, the 

 fifth , the wing is pushed 

 out from the wing-poc- 

 ket, and Hes under the 

 old larval cuticula dur- 

 ing the prepupal sta- 

 dium. It is then of 

 the form shown in 

 Figure 216, /. The 

 molt that marks the 

 beginning of the pupal 

 stadium, exposes the 

 wing-buds, which in 

 the Lepidoptera be- 

 come closely soldered 

 to the sides and breast 

 of the pupa. Imme- 

 diately after the last 

 molt when the adult 

 emerges, the wings 

 Fig. 216.— Several stages in the development of the expand greatly and 

 wings of a cabbage butterfly (After Mercer). assume their definitive 



form. 



While this increase in size and changes in form of the developing 



wing are taking place, there occur other remarkable developments in 



its structure. A connection is made with a large trachea near which 



the histoblast is developed, shown in cross-section in the first four 



