March, 1905.] Powell: Wings of Certain Beetles. 



THE DEVELOPMENT OF WINGS OF CERTAIN 



BEETLES, AND SOME STUDIES OF THE 



ORIGIN OF THE WINGS OF INSECTS. 



By P. B. Powell. 

 Stanford University, Calif. 



( Continued from Vol. XII, page 24J. ) 



The downward growth of the wing continues until early in the 

 prepupal period, when it reaches the base of the leg bud, which pre- 

 vents further growth in this direction (Figs. 8, 21). The wing now 

 exists as a double-walled pad lying between the hypoderm and cuti- 

 cle, extending downward and backward, as far as the base of the leg 

 and with the basement membranes of the two layers usually closely 

 pressed together, except at the places where tracheae have entered the 

 wing, forming vein cavities. The nuclei of the two walls still lie at 

 several different planes and the outer (upper) wall is somewhat the 

 thicker, while the bases of the cells are abruptly narrowed and thread- 

 like. 



The later stages in the development of the wings of T. plasto- 

 graphus and of D. va/ens are very much as have been described by 

 various authors for the Coleoptera and Lepidoptera. With the begin- 

 ning of the prepupal period the growth of the wing becomes acceler- 

 ated. With the lengthening of the wing the nuclei begin to be drawn 

 up into one row near the outer ends of the cells, while the cells them- 

 selves become very much elongated and drawn out in places (Figs. 9, 

 10). Shortly before pupation this process becomes completed and 

 the cells have the characteristic "fringed" appearance of the pupal 

 hypodermis described by Verson (1904). The wing is now greatly 

 wrinkled and folded, the vein cavities are greatly enlarged and filled 

 with haemolymph and leucocytes, both of which also circulate in the 

 spaces between the elongated cells. The basement membrane, which 

 throughout the development of the wing is very thin and not easily 

 discernable, becomes more or less degenerated during the prepupal 

 period and in places the bases of the cells either end free (Fig. 19), 

 or become fused and anastomosed with each other (Figs. 11, 22). 



Early in the last stage there is secreted all around the body, under- 

 neath the dense outer chitin, an inner layer of soft spongy or stringy 



