Centrifugal Force upon Beetles^ E,ggs 52 1 



colorless cap at the outer end. The sections show it to consist of 

 a small mass of gray material which is heavier than the large 

 yolk-globules. I shall call this the gray cap. It is composed of 

 very small granules, does not stain like yolk nor as intensely as 

 the cytoplasm of the "Keimhautblastem." The pole-disc has 

 moved forward during the second hour the egg was centrifuged, 

 and now lies anterior to its original position about one-fourth of 

 the total length of the egg. In its progress it has pushed its way 

 forcibly through the yolk mass, leaving a long, narrow, open path- 

 way behind it (Fig. 12, pt). No nuclei were found in the sec- 

 tions. 



C.B. ^, /. This egg was centrifuged for four hours and then 

 fixed. A surface view of the egg stained in toto revealed a large 

 central, colorless bud at the posterior (inner) end surrounded by 

 a number (at least seven) of smaller buds. These are produced by 

 wrinkles or folds in the surface of this region, due either to poor 

 fixation or to a decrease in turgidity at the inner end. The entire 

 egg seems to have been shortened slightly antero-posteriorly by the 

 continued application of centrifugal force. The longitudinal sec- 

 tions made of this egg are not perfect, certain portions of the outer 

 end being lost because of the accumulation of large yolk-globules 

 (yolk which is not imbedded in cytoplasm is liable to break on the 

 knife in cutting). I cannot be positive, therefore, of the presence 

 of a gray cap in this egg. There is little doubt, however, that this 

 structure was not absent in this instance, since the other eggs 

 similarly treated possess a gray cap. The vesicular zone has 

 increased in size during the last two hours this egg was centrifuged, 

 and has been folded into larger bud-like prominences than were 

 noted in the last egg described (C.B. 4, e). The pole-disc has 

 made further progress in its journey away from the inner end. 

 It has now reached a point about one-third of the total length of 

 the egg anterior to its original position (Fig. i^,gc. d). The open 

 pathway which was observed behind it in C.B. 4, ^, has become 

 closed and the "Keimhautblastem" that was pulled in with it has 

 passed back and taken part in the vesicular layer. 



C.B. ^, g. A normal larva hatched from an egg centrifuged 

 for fifteen minutes with the posterior end towards the axis of rota- 



