BY R. ,J. TILTA'AKl*. 



547 



We may sum up the above results as follows: — 



(1) Orders in which the pupal wings are holotracheate : — 



(A) Alar trunk not always quite complete ; position of trachea 

 M upon it variable ; very strong tendency towards splitting 



' back of all tracheae. LEPIDOPTERA. 



(B) Alar trunk complete ; position of trachea M about midway 

 along it between the costo-radial and cubito-anal groups ; 

 little or no tendency towards the splitting back of the 

 trachea? MEGALOPTEEA and PLANIPENNIA. 



(2) Orders in which the pupal wings are merotracheate :— 



(C) Alar trunk complete ; more than two trachea? enter the 

 wing ; a true costal trachea frequently present. 



DIPTERA. 



(D) Alar trunk incomplete ; only two tracheae enter the wing, 

 one from the costo-radial and one from the cubito-anal 

 group ; generally no costal trachea. * 



(a) The anterior trachea is R, the posterior M. 



MECOPTERA. 



(b) The anterior trachea is R, the posterior Cu or 1A ; or 

 both may penetrate aimlessly into the wing-sheath. 



TRICHOPTERA. 



It will be clear,, from the characters studied in this section alone, 

 that the Trichoptera, as the most" highly specialised of all the 

 Orders in the evolution of its pupal tracheation, cannot be re- 

 garded as ancestral to any other Order now existing. Nor can 

 the Mecoptera possibly be ancestral to any Order except the 

 Trichoptera; and this only by supposing that the Trichopterous 

 condition could be naturally derived from the Mecopterous, as 

 a further specialisation. As we shall see in the sequel, there is 

 at least one venational character in which the Trichoptera are 

 more archaic than the Mecoptera; and thus they cannot be de- 

 rived from these latter. 



Section ii. The Main Veins and their Branches. 

 (Text-hgs. 37-40.) 



In their hypothetical ancestral type of tracheation for the Insect 

 Wing, and consequently also for the venation (which originally 

 coincided with the tracheation in so far as the main veins were 

 concerned), Comstock and Needham (14) indicated the following 

 conditions for the trachea? and veins : — 



*I have seen a costal trachea in imaginal icings of some Trichoptera, 

 but never in the pupal wings. 



