196 



.47V INTRODUCTION TO ENTOMOLOGY 



portions 

 stadium, 



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

 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 lies 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 

 I 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 

 wings of a cabbage butterfly (After Mercer). 



expand greatly and 

 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 



