March, i 9 o S .] Powell : Wings of Certain Beetles. 17 



part of the spiracles. The metathoracic wing disc is not situated over 

 the tracheal center of its segment, while the remains of the meta- 

 thoracic spiracle does lie over this center. The mesothoracic spiracle 

 has migrated forward into the prothorax, but it is evident that not 

 only the opening but the spiracular disc, as well as the tracheal center 

 have migrated forward. Moreover, the metathoracic spiracle has not 

 migrated, or at least very slightly, as will be seen by comparing its 

 position with that of the first abdominal spiracle ; so that it is not 

 possible that either the meso- or metathoracic wing should have arisen 

 from any part of a spiracle. 



While, among many of the orders of insects, the metathoracic 

 spiracle is in a more or less vestigial condition, being either consider- 

 able smaller, or entirely degenerated, it is to be found in the Hymen- 

 optera, full sized and perfectly formed. In this order the positions 

 of the wings and the spiracles in respect to one another are different 

 from anything that I have found in any of the other orders. In the 

 larva of the honey-bee {Apis mellifica) the metathoracic spiracle is as 

 large as any of the other spiracles and cannot be distinguished from 

 them in shape. The meso- and metathoracic spiracles and the ab- 

 dominal as well occupy positions on the pleurum near the front margin 

 of their respective segments, while the wings are centrally situated 

 on their segments and arise considerably below the spiracles, as may 

 be seen by reference to Figs. 28, 29. This is just the reverse of their 

 position in the Coleoptera and Lepidoptera, in which, I have 

 shown (Fig. 27), the wing discs are distinctly above a line drawn 

 through the spiracles, while in Apis, the base of the wing bud is below 

 the spiracles, at about one third the distance between them and the 

 leg buds (Figs. 28, 29). This can be easily seen by an external ex- 

 amination of the larva, as the wing and leg buds lie outside the hypo- 

 dermis, next the cuticle and can be readily seen through it. The 

 tracheal centers under each spiracle are greatly reduced, there being 

 only a few small branches which soon break up into a fine network of 

 small tracheae or tracheoles. We find in Apis, just as we did in the 

 Silkworm, a small trachea running from the tracheal center behind 

 each wing bud and meeting at the base of the bud a similar trachea 

 coming from the tracheal center in front of the wing. I believe this 

 will be found true of all winged insects, while from these two tracheae 

 evidently develop, respectively, the two groups of wing tracheae. 



