March, 1905.] Powell: Wings of Certain Beetles. 7 



{a) The Tracheoles. — In all the larva: that I have examined there 

 is from the very beginning a close connection between the wings and 

 the tracheal system. Comstock and Needham found (in Hippodamia 

 13-punctatd) that the wing fundament had at first "no connection 

 with or approximation to any trachea," this connection not occurring 

 until the wing disc had invaginated well into the body, approaching 

 a lateral tracheal trunk, and evagination had begun. Needham found 

 that in Mononychus vtdpeculus the wing bud differed from the leg bud 

 only in having no tracheae at or near its inner surface. This I think 

 is an unusual condition and not to be found in many Coleoptera. In 

 all the Coleopterous larva? examined by Tower (1903), even in the 

 earliest stages the wing fundament received a distinct branch from the 

 tracheal trunk ; a similar condition was found in the Lepidoptera by 

 Mercer (1900). 



In the earliest stages of the wing, in T. plastographus and D. 

 valens and in a Buprestid, even before the fundament becomes recog- 

 nizable in some specimens, two branches extend from the tracheal 

 trunk to the hypodermis at the place where the wing fundament is 

 shortly to arise. Sections of larvae taken at this time show the tips 

 of these tracheal branches abutting directly against the bases of the 

 cells of the newly forming wing, the tracheal cells proliferating and 

 spreading out over the inner face of the disc. A mass of cells is thus 

 formed, the walls of which are either very thin or more or less de- 

 generated and in this mass of cytoplasm and nuclei, forming tracheoles 

 are to be seen (Figs. 2, 3, 23). In some cases (T plastograplius') 

 the tip of the tracheal branch, when it touches the wing disc, ap- 

 parently pierces the basement membrane (Fig. 5) and then spreads 

 out directly against the bases of the cells of the disc as a mass of cells, 

 in the cytoplasm of which tracheoles are developed as fine somewhat 

 coiled tubes (Figs. 5, 6). In other specimens the basement mem- 

 brane apparently degenerates so that the bases of the cells of the disc 

 are free. I have seen this in D. valens (Fig. 23). Occasionally the 

 tracheae push into the disc so that they are nearly surrounded by the 

 cells of the latter (Fig. t). Fig. 5 ( T. plastographus) is a section 

 through the disc of the fore wing near its cephalic margin, just after 

 the last moult and shows a tracheal branch pushing through the base- 

 ment membrane and spreading out under it. 



My observations confirm those of Tower and Mercer that the 

 tracheoles are formed from the cytoplasm of the tracheal cells and not 



