co8 KNOWER. [Vol. XVI. 



open a nest, the passages which traverse it in all directions 

 are seen to have no regular arrangement. The walls of the 

 inner passages are thinner than those at the surface. The 

 queen is generally found in the interior of the nest, near its 

 base, surrounded by numerous workers and larvae, and not far 

 from the eggs. The eggs have been collected into heaps, by 

 the workers, as they were laid, and piled up without any appar- 

 ent system in the passages near the queen. The older larvae 

 also assist in caring for the eggs. It is an easy matter to col- 

 lect quantities of eggs, since they are quite moist and adhere 

 together in masses, in which all stages of development are to be 

 found, from unsegmented ova to larvae emerging from the egg- 

 membranes. Considerable time must be subsequently devoted 

 to picking out stages from such mixed material. 



The unsegmented egg is about 0.5 mm. long by 0.22 mm. in 

 the shorter diameter. It is elongated, larger at one end, and 

 markedly convex on one side. This shape makes it easy to 

 determine the planes of symmetry from the start, since the 

 enlarged or mycropylar end is found to be the posterior pole, 

 while the convex side is the ventral surface. In the course of 

 its development the embryo changes its position by a remark- 

 able process of " revolution," like that described for the Libel- 

 lulids and certain primitive Orthoptera. This must be kept in 

 mind in speaking of the anterior and posterior poles, and of the 

 dorsal and ventral surfaces. As used above, the micropylar 

 end of the egg is the definitive, as well as the primary, posterior 

 pole, and the convex micropylar side becomes the final ventral 

 surface. 



It will appear that the embryonic rudiment when first estab- 

 lished, and until shortly after the closure of the amniotic cavity, 

 lies entirely on the convex ventral surface of the yolk. At this 

 period the entire embryo occupies but a small area on this sur- 

 face, just beneath the micropyles, at its extreme posterior limit, 

 the hind end of the germ-band reaching the posterior pole of 

 the egg. 



In the last stages of development the same relative position, 

 lost during intermediate changes, is reestablished by "revolu- 

 tion," so that the posterior end of the embryo comes again to 



