1909] Homologies of Wing Veins 123 



then, which was caused when mount after mount of Dactylopius 

 sp. on cactus showed five very deHcate but perfectly distinct 

 tracheae. See Figure 42. 



Four of these tracheae are simple and uncoalesced to the base 

 of the wing. They are arranged in two groups, the base of the 

 subcostal, radial and medial tracheae lying close together and the 

 cubital and first anal tracheae forming the other group at a little 

 distance from the first. 



The subcostal and radial tracheae are both very wavy and as 

 they lie close together, they cross and recross, often for the 

 greater part of their length. 



The medial trachea takes a median course. This consists of 

 two interwoven branches, pursuing a common course. 



The tracheae in the wing of this coccid remain distinct until 

 after the veins begin to form so that the relation of the two is at 

 once discerned.- One vein follows the general trail of the sub- 

 costal and radial tracheae. This vein very evidently represents 

 radius. 



The second vein follows the base of the first tracheal group to 

 about the point where the medial tracheal separates from the 

 subcostal and radial. The vein here takes a direct line for the 

 middle of the caudal margin of the wing. For slightly less than 

 one-third the length of this vein it frequently joins the path of the 

 cubital trachea. This corresponds most closely with media. 



Besides these two main veins a short spur representing the 

 subcosta is present. 



In a wing so highly specialized as the coccid wing it is not 

 improbable that the tracheation has lost its value as a basis for 

 the venation. Certainly in the species studied there seems no 

 necessary connection between the trachece and the veins which are 

 found later. 



In Pseudococcus citri the tracheation was exceedingly dif^- 

 cult to trace. The same veins occur in this species (fig. 41) as 

 in the preceding (fig 43). 



In many species of Coccids there are shadowed portions of the 

 wings. It is due to this fact that we find the coccids sometimes 

 figured with apparently four long veins, alternately dark and light, 

 as for instance, in Westwood.* 



* Westwood, J. O. Arcana Entomologica. Vol. I, Plate 6. 



