570 



HOMES WITHOUT HANDS. 



In the accompauying illustration three most remarkable nests 

 are given, aU of them the work of hymenopterous insects, and 

 aU serving in some degi'ee to illustrate the hexagonal system of 

 cell-building, so common among the hymenoptera. 



MISCHUCVTI-AKIIS 



RAPHIOASTEft. 



Of these, perhaps, the central figure is the most interesting, 

 because it entirely sets at rest a question which is periodically 

 agitated. It is made by an insect belonging to the genus Icaria,. 

 Perhaps my readers may remember that on page 429, the cele- 

 brated bee-ceU problem is described, and that mention is made 

 of the many theories which have been invented to solve the 

 riddle. Among them the two most conspicuous are those which 

 are known as the equal pressure theory and the excavation 

 theory. Differing as they do in many respects — one attempting 



