Saw-Flies. 



179 



something like very thin and flimsy grey paper. Conse- 

 quently, they must press strongly upon each other, and we 

 might reasonably expect to find that their angles are well 



and boldly developed. But, instead of that, we find that they 

 have no angles at all, but remain smooth and rounded, 

 throughout their length. 



[Perhaps the most powerful argument against the equal 

 pressure theory is to be found in the nest of a species of 

 Icaria, which is shown in the accompanying illustration. 



[As may be seen by reference to the illustration, the 

 material of which they are made is so soft, that they bend 

 over by their own weight, and therefore we might expect to 

 find that they would follow the shape of the Raphigaster 



