Centrifugal Force upon Beetles^ E,ggs 525 



C.B. p, h. Three zones are recognizable in this egg corre- 

 sponding to those already described in egg C.B. 4, e and, although 

 centrifuged for six hours, no noticeable difference is discernible in 

 the distribution of material in this egg and one of nearly the same 

 age which was centrifuged for only one hour (C.B. 2, h). The 

 nuclei of many of the vitellophags are distorted or disintegrating. 

 The granules of the pole-disc have, as in normal eggs, become 

 imbedded in the cytoplasm of the primordial germ cells; the latter 

 occupy their usual position at this stage between the vitelline mem- 

 brane and the blastoderm at the posterior pole. 



C.B. p, c. Two eggs were fixed forty-one hours after they were 

 taken from the centrifugal machine. One of these did not develop, 

 its nuclei disintegrating and the "Keimhautblastem" becoming 

 vacuolated; the other carried an embryo with a distinct ventral 

 groove (Fig. 15). Superficially this embryo resembles that of a 

 normally developed egg of this age except that it does not reach as 

 far anteriorly on the ventral surface, but extends farther around 

 the posterior end and up on the dorsal surface (compare Figs. 4 

 and 15). It is evident that under the influence of centrifugal 

 force the nuclei and "Keimhautblastem" have become massed in 

 the posterior half of the egg, where development has continued. 

 This egg if it had been allowed to develop would no doubt have 

 produced an embryo resembling that described under CM. i, b 

 (Fig. 21). Sections of this egg show a rearrangement of the yolk- 

 globules, a condition being reached similar to that illustrated in 

 Fig. 9. The gray cap and vesicular zone are still present. 



C.B g, d. One of two eggs preserved sixty-five hours after 

 being taken from the centrifugal machine did not develop; the 

 other produced a shapeless mass of tissue, no definite organs being 

 distinguishable. Fig. 16 is a diagram of a sagittal section through 

 this egg. The gray cap and vesicular zone are still present, the 

 former at one side of the outer end of the egg, the latter just 

 dorsal to the embryonic tissue. 



