The Development of the Whigs of a Caddis-fly Platyphylax designatus Walk. 577 



pigment and in another place says: "In the embryo of Leptinotarsa 

 decemlineata, shortly before hatching, or in the newly hatched larva 

 the wing discs will be found lying beneath spots of black pigment on 

 the sides of the last thoracic segments." In Platyphylax we called 

 attention to the darkened cuticula lying over the wing rudiment but 

 this darkening is in the color of the cuticula itself and not due to pig- 

 ment. In the older larvae this darkened area was always directly 

 exterior to the wing rudiment and could easily be followed back from 

 the older to the very youngest larvae making it clear that in the latter 

 the hypodermis adjacent to this darkened area was the exact position 

 at which the wing rudiment would later appear. It was also found 

 that in the mesothorax the wing rudiment occupies a more dorsal 

 Position within the pocket than it does in the metathorax. This region 

 where the wing rudiment first appears and where it later develops 

 we shall call the area of the wing rudiment. 



An examination of sections of very young larvae, soon after hatch- 

 ing, shows that the hypodermis within the pocket is everywhere the 

 same and that it is also similar to that which Covers the rest of the 

 body, Landois (6), Tower (16). The hypodermis consists of a thin 

 layer of protoplasm containing small ovoid nuclei which lie flat against 

 the surface of the cuticula. The layer of protoplasm was in nearly every 

 place thinner than the transverse diameter of any nucleus it contained 

 and, in many places, it consisted of a mere Strand connecting one nu- 

 cleus with another (Fig. 1 Hyp). A careful examination of sections 

 of more than twenty of these young larvae showed but a single mitotic 

 figure in the hypodermis within the area of the wing rudiment, and, 

 over the entire surface of the entire meso- and metathorax, but few 

 dividing nuclei could be found. In these youngest larvae the muscle 

 forming the inner boundary of the pocket was already formed and the 

 fat body which lies between it and the outer wall could be easily found 

 (Fig. 1, M and Fl). In the transverse sections of the larvae this fat 

 body was very small. 



It may be well to mention in this place two other ways in which 

 the area of the wing rudiment can be distinguished from other parts 

 of the thorax; neither of these are noticeable in the very youngest 

 larvae, but in all others. Sections of the two wing-bearing segments 

 show that in the hypodermal cells there are many pigment granules; 

 these are not present in those cells within the area of the wing rudiment 

 (Fig. 4). The sections also show the thoracic cuticula to be more or 



