1909] Homologies of \Vi}ig Veins log' 



wings immediately after emergence. Handlirsch* thus mistook 

 this forming vein for a trachea in his preparation of Schisoneura 

 lanigera. 



Wherever there has been the sHghtest chance that a subcostal 

 trachea might be present, exhaustive investigation has been made 

 until no possible doubt of its absence remained. 



Again, for some species, one of the secondary branches of the 

 radial trachea near its base might easily be mistaken for a sub- 

 costal trachea so far as its position goes. Chermes pinifoli(F 

 (fig. 26) serves as an illustration of this. But these secondary 

 branches are very variable even for the same species and after 

 examining large series of mounts little difficulty is experienced in 

 distinguishing the tracheae of the main veins from secondary 

 branches. 



The only trachea found during the whole time possible to- 

 interpret as the subcosta was a single mount out of hundreds 

 of Mindarus {ahietiniis Koch ?) where an exceedingly short branch 

 from the radial trunk near the base occurred, larger than the 

 ordinary secondary tracheae. This may be an abortive subcostal 

 not entirely atrophied. Or it may be merely an abnormality. 



This species of Mindarus, collected in great abundance from Balsam fir 

 in the vicinity of Orono is apparently the same as ahietinus Koch. But as it 

 has not yet been compared with specimens from Europe it is given in this paper 

 accompanied with a question inark. 



Another opportunity for confusing a branch of the radial 

 trachea for a subcostal trachea is found in wings where the path 

 of the tracheal branch of radius chances to coincide with that of 

 the newly forming subcostal vein. Such a case is shown in the 

 tracheation of Pemphigus acerifolii (fig. 12) where the trachea 

 follows the stigmal margin that the subcostal vein is later to 

 bound. But the branches of the radial trachea are quite as likely 

 to cut directly across the path of the forming subcostal vein as to 

 coincide. Chermes abietis (fig. 24) will illustrate this. 



The point, however, which gave me most trouble was the fact 

 that very frequently the fold in the wing caused by the forming 

 subcostal vein bent the branches of the radial trachea to such an 

 extent that their connection with the radial trachea was obscured 

 and a series of tracheal branches resulted which had every appear- 

 ance of rising directly from the region of the subcosta. 



* Handlirsch, A. Fossilen Insekten. Plate VIII. Fig. 9. 



