Tlie Development of the Wings of a Caddis-fly Platyphylax designatus Walk. 589 



throiigh which the internal wing rudiment can reach the outside. While 

 not being able to give any good new explanation of the enlargement 

 of the opening nothing has been noticed corresponding in any way 

 to the fusion above mentioned. My sections were all cut through 

 only a part of the body and it was thus impossible to study the re- 

 lative diameter at different stages or to notice, if there was any, change 

 in the hypodermis at other parts of the body. During the stage we 

 have been describing, as well as in others, a large amount of exuvial 

 fluid was noticed but does not, as far as we can see, have anything to 

 do with the growth of the wing rudiments or their expulsion from the 

 peripodial cavity. 



All the speciniens examined indicate that the wing rudiments do 

 not become external until after the larva has closed its case prepara- 

 tory to pupation. Of all the larvae studied before the closure of the 

 case there was not a single one but that showed the wing rudiments 

 still within the peripodial cavity. The only exact data that can be 

 given on this point is as f ollows : two larvae were killed ten hours after 

 the final closing of the case, both of these were examined and showed 

 small external wings; in each case these were very similar to figure 17 

 which is the youngest specimen found with all the wing rudiments 

 external. It would therefore appear that in Platyphylax the wings 

 rudiments do not become external until after the larva has entirely 

 closed its case. The wing after its expulsion from the peripodial cavity 

 shows that its outline and the markings upon it have become much 

 more regulär (Figs. 17 and 20) and it now lies nearly straight and parallel 

 to the cuticular layer of the body (Fig. 18). Within the pocket the 

 conditions are similar to those found in the earlier stages except in the 

 change of the rudiment itself. The two layers of the wing have been 

 more or less separated from each other (Fig. 15^) by the Spaces be- 

 tween them, developing wing veins, which have heretofore been some- 

 what irregulär and not sharply defined. These Spaces are in the ex- 

 ternal wing more regulär (Fig. 17^) and continue to become more so 

 until each developing wing vein is clearly defined (Fig. 21). 



CoMSTOCK and Needham (2) have called attention to the reduc- 

 tion of the tracheae in the developing wing of the Trichoptera. This 

 is clearly shown in Platyphylax; so far in the development no tracheae 

 have been found in the wing although the wing veins and the areas 

 between them have now become clearly defined and noticeable both 

 in surface view and in section, The developing wing veins contain 

 a number of leucocytes. The two layers of hypodermal cells, except 



