626 



THE PANORPOID COMPLEX. 



Part 2. The AViNn Trichiation and its Relationship to the 

 General Scheme of Venation. 



By R. J. TiLLYAHD. M.A.. D 8c., F.L.S., F.E.8., Linnean 

 Macleay Fellow of the Society in Zoology. 



(Plates Ixvii.-lxix., and Text-figures 17-^14). 



If we cut off a small portion of the wing of any archaic Holo- 

 metabolous Insect, such as, for instance, Archichaiiliodes guttiferufi 

 Walk., (Text-fig. 22) of the Order Megaloptera, and make a 

 cleared mount of it, ^ve shall find that, when it is examined 

 under a high power, both veins and membrane of the wing are 

 covered with hairs. These hairs will be seen to be developed 

 equally abundantly upon the upper and under sides of the wing. 



This covering of hairs may be spoken of collectively as the 

 Winy-trichiatimi. Though it is to be found in all Orders of the 

 Holometabola, it does not occur in all Orders of Insects. It isj 

 for instance, entirely absent from the wings of the Odonata. 



Generally speaking, there may be found upon the wing of any 

 Holometabolous Insect two types of hairs, which I have already 

 named microtrichia and macrotrichia respectively (5). These may 

 be defined as follows: — 



Microtrichia (Gr. [xiKpo's, small; and Opi^, r^txos, a hair) are 

 minute hairs, generally much curved or hooked, which are de- 

 veloped in connection with every unspecialised hypoderm-cell of 

 both upper and under surface of the wing. Hence the}^ occur 

 indiscriminately and exceedingly abundantly upon veins and 

 membrane alike. Theii- bases of insertion appear as simple 

 circular pits, in which, under a very high power, a central per- 

 foration leading into a very small lumen in the interior of the 

 hair can be made out. They vary in length from under l/u to 



