288 



IXSECT ARCHITECTURE. 



that leaves are only an accidental, and not a necessary, part 

 of the structure. AVhen a leaf happens to be in the line of 

 the walls of the nest, it is included ; but there is no appa- 

 rent design in pressing it into the service, nor is a branch 

 selected because it is leafy. On the contrary, by far the 

 greater number of these nests do not contain a single leaf, 

 but are composed entirely of grey silk. In external form, 

 no two of these nests are alike ; as it depends entirely upon 

 the form of the branch. When, therefore, there is only one 

 t^^dg, it is somewhat egg-shaped; but when there are 

 several twigs, it commonly joins each, assuming an angular 

 shape, as may be seen in the preceding figure. 



This irregularity arises from the circumstance of each 

 individual acting on its own account, without the direction 

 or superintendence of the others. The interior of the struc- 

 ture is, for the same reason, more regular, being divided 



Winter nests of Porthe^ia chrysorrliaa, one being cut open to show the chambers. The 

 dots represent the egesta of the caterpillars. 



into compartments, each of which forms a chamber for one 

 or more individuals. Previous to the cold weather, these 

 chambers have but slight partitions ; but before the frosts 

 set in the whole is made thick and warm. 



