The Development of the Wirgs of a Caddis-fly Platyphylax designatus Walk. 587 



in length; second, above these there are, running in the same general 

 direction, two to five other lines. 



A study of sections at this stage shows that there are no thickenings 

 or foldings of the rudiment that would cause the markings to appear in 

 surface view. It was however noticed that at this stage where the 

 markings were visible sections show that the two hypodermal layers 

 forming the rudiment are at places pulled away from each other, this 

 makes the double layer continuous between the open Spaces and 

 naturally darker in surface view (Fig. 15^). The greater coniplexity 

 of the markings whtch comes in an older stage is due to the above 

 fact and also to the folding of the rudiment which later takes place. 



With the exception of the earliest stages the wing rudiment has 

 thus far been of a kidney shape but, soon after the appearance of the 

 markings, the outline begins to change and becomes much more irre- 

 gulär. Both of the rudiments may change at the same time or it often 

 happens that specimens are found in which one rudiment retains its 

 younger form after the markings have, on the other one, become more 

 advanced in their development (Fig. 15). However great these irre- 

 gularities in form may become the rudiment is always more concave 

 on the anterior margin and it is near this margin that the peripodial 

 pore is still seen; this has become a long narrow and very irregulär 

 slit and, from a surface view, it is often difficult to find: a study of 

 sections will always show that it is present. In the growth of the 

 rudiment the anterior margin, as just noted becomes more curved 

 and irregulär, the lip becomes bent and more or less hides the pore, 

 especially in a flat surface view. The markings and foldings of the 

 rudiment soon become very complex, due to the irregulär growth 

 and folding of the rudiment. In Platyphylax, as has been noted in 

 other insects, the shape of the rudiment is somewhat influenced by 

 its pressure against the base of the leg; often this at first causes an 

 indentation along the margin to be foUowed later by a bending of 

 the rudiment. 



Most of the rudiments pass through a stage in which their shape 

 is somewhat similar to the left hand figure represented in figure 15, 

 this is about the greatest proportional width that they assume. The 

 next change is generally one of elongation which admits of many 

 variations in the shape of the rudiment. It often happens that the 

 lengthening goes on so that there results at one or both ends a pro- 

 truding lobe. 



At just what period in their development the wing rudiments of 



