\ 



THE WINGS OF TRICHOPTERA 



311 



Rhyacophila are lettered in accordance with this interpretation (Betten 



'13.) 



During my studies of this subject Dr. Betten has aided me in every 

 possible way, placing in my hands portions of his manuscript and figures 

 and many mounted wings. I am under great obligation to him for this 

 assistance. 



{d) THE MORE GENERAL FEATURES IN' THE SPECIALIZATION OF THE WINGS 



OF THE PHRYGANEINA 



The wings of Rhyacophila Juscnla (Fig. 320) probably resemble very 

 closely the wings of the primitive Trichoptera, as they resemble in their 

 more general features the hypothetical primitive type of insect wings. The 

 more important modifications of this type are the following. 



In the fore wing the tips of the second anal vein and two of the branches 

 of the third anal vein coalesce. This is a distinctively characteristic 

 feature of the wing-venation of the Trichoptera. The subcosta bears an 

 accessor}' vein; this, however, is unimportant; accessory veins borne by 



SC^ Si2 



Cu2 Cu\ 

 Fig. 321. — Fore wing of Rhyacophila sp. 



the subcosta exist in only a few genera of this order; in some there are 

 several of these veins, as in the Japanese genus Perissonetira, figured by 

 Ulmer ('07). The coalescence of veins Cu and ist A at the base of the wing 

 and the formation of the serial vein consisting of the base of media, the 

 posterior arculus, and the distal part of vein Cu is an ordinal characteristic. 

 In the hind wings media has been reduced to a three-branched condition by 

 the coalescence of veins M3 and AI4. 



By comparing more specialized forms with Rhyacophila fnscnla it will 

 be seen that in the preanal area the specialization of the venation of the 

 wings is always by reduction. In the anal area of the hind wings the 

 speciahzation is in some cases by addition, resulting in a broadly expanded 

 anal area, in others it is by reduction. It is unnecessary to indicate, in this 

 place, the methods of specialization of the wings in the different families of 

 this order, as this has been done by Ulmer, Betten, and others. 



