THE DEVELOPMENT OF THE HAIRS UPON THE WINGS 
OF PLATYPHYLAX DESIGNATUS WALK. 
By WM. S. MARSHALL, University of Wisconsin. 
While it has been assumed that the hairs on the wings of the 
Trichoptera develop in exactly the same way as those upon the 
wings of the Lepidoptera there is, so far as we know, no definite 
work to show that this assumption is correct. The following 
study was therefore undertaken to definitely ascertain, in some 
one species of Trichoptera, in what manner these hairs did 
develop upon the surface of the wings and Platyphylax designatus 
was selected for the work. 
It has been impossible to find any works which could be 
given as an historical review of the subject and those papers 
having to do with the development of the wing of the caddis- 
flies have been given in a former paper (5). Dewitz (3), from 
whose work comes most of our previous knowledge of the devel- 
opment of the wings in this group of insects, does not take up 
the formation of the wing hairs. Spuler (9) distinguishes 
between hair scales and those hairs without a circular ring-like 
base for articulation and he shows a surface view of a portion of 
the wing of a Trichopteran, Philopotamus scopulorum, with a 
few of the latter hairs and four of the ring-like bases into which 
the hair scales are inserted. Regarding these structures he says: 
“Die gleichen Gebilde (hairs) finden wir auch bei den Trichop- 
teren, gerade die Micropteryginen und Hepialiden, in der 
Fligelbidlung so nahe den allgemeinen Modus der Haarbildung 
vor sich. Dieselben werden von der Hypodermis gebildet. 
Jeder Stachel ist seiner Bildung nach unicellular.’’ Tower (11) 
reaches a similar conclusion, saying: ‘“‘In development the 
scales of Coleoptera follow exactly the same course as was found 
by Mayer (6) in the Lepidoptera.” 
The wings of Platyphylax designatus are more or less covered 
with hairs; these are present upon all the wings and on both 
surfaces although the anterior wings show a greater degree of 
pubescence than the posterior and the upper surface bears a 
much larger number of hairs than the lower. These hairs can 
be roughly divided into four groups: 1, vein and marginal hairs; 
2, large surface hairs; 3, small surface hairs; 4, special long hairs. 
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