The Development of the Wings of a Caddis-fly Platyphylax designatus Walk. 593 



in the former segment the lateral margin is more clearly defined. At- 

 tention has been called to the two dark cuticular spots which appear 

 on the cuticula over the developing wing rudiment and to the fact 

 that these cannot be seen in the newly hatched larva (Fig. 27) in a 

 surface view. These cuticular spots soon appear and one can than 

 easily see, especially in the mesothorax, that the developing wing rudi- 

 ment lies under the dorsal plate and somewhat above its lateral margin 

 (Fig. 28 at *). In the last larval skin (Fig. 29) the same thing can 

 be seen but here the wing rudiment lies a little nearer the lateral margin 

 of the dorsal plate than in the earlier stage. It would appear that 

 when the wing becomes external its position would be between the 

 tergum and the pleurum. 



Summary. 



The wing rudiments of Platyphylax first appear in the larva soon 

 after hatching, probably second instar, and are noticed as small disk- 

 like thickenings of the hypodermis lying each under a small dark 

 marking of the cuticular layer. 



Each disk invaginates and, in sinking below the surface, forms 

 a peripodial cavity which communicates with the outside by a peri- 

 podial pore. The disk is at first circular but soon elongates and then 

 lies oblique to the longitudinal axis of the body of the larva. 



The cuticular layer just over the rudiment differs from the sur- 

 rounding part in being darker and free from small setae. The cuti- 

 cular layer is secreted at all stages by the cells of the rudiment. 



The disk evaginates and soon grows so large that a folding of 

 the rudiment within the peripodial cavity is necessary. 



The peripodial pore becomes a long narrow slit through which the 

 wing rudiment leaves the peripodial cavity and becomes external. 



AVhile still within the peripodial cavity dark markings appear 

 upon each rudiment, this forms alternating light and dark areas upon 

 the wing; the former become the wing veins and the latter the areas 

 between them. 



Tracheae do not enter the developing wings until they have be- 

 come external and the wing veins have been formed. 



The wings become external soon after the larva has closed its 

 case for pupation. 



Each wing rudiment is situated under the dorsal plate a little 

 above its lateral niargin. 



Zoological Laboratory, University of Wisconsin, January, 1913. 



