124 ELEVENTH REPORT. 



approached. The orientation of the egg has no effect upon the production 

 of these zones since they appear when either the anterior or the i)osterior 

 pole is toward tlie center of rotation. When centrifuged eggs are fixed 

 inimecUately after being talven from the macliine they exhibit in sections 

 three regions which (Uffer greatly in their composition. The bright orange 

 zone of the living egg is seen to be made up of irregular oil globules imbedded 

 in cytoplasm which has risen to the light end of the egg. I have given to 

 this the name "vesicular zone." The colorless cap at the outer end is com- 

 posed of a homogeneous mass of granules, the heaviest substance in the egg, 

 which has been driven to the pole away from the center of rotation. I 

 have called this material the "gray-cap." Where the substance of the gray- 

 cap comes from is not known. The comparatively large intermediate zone 

 is a mass of yolk globules, the large heavy spheres being at the outer end 

 and the smaller granules blending with the cytoplasm of the vesicular zone. 

 The nuclei are lighter than the yolk and of about the same specific gravity 

 as cytoplasm. They all concentrate near the inner pole carrying with them 

 the little islands of cytoplasm in which they are normally embedded. Nuclear 

 division proceeds as usual showing that the mitotic figure is not easily 

 disarranged. The germ-cell determinates are heavier than the nuclei and 

 the cytoplasm and move en masse toward the end away from the center of 

 rotation. 



The eggs of the 1_:)eetles differ from the eggs which ha^'e previously been 

 centrifuged in the absence of cell Avails in the early cleavage stages. It is 

 thus possible to obtain results with older eggs and to extend investigations 

 iiito later developmental stages. Moreover there are no cell walls to hinder 

 the restitution of the substances which have been thrown out of their normal 

 positions. It has been found that "when different substances of the egg are 

 displaced by strong centrifuging they tend to come back to their normal 

 positions unless prevented by partition walls which have formed in the 

 meantime." (Conklin, 1908, p. 94). In beetles' eggs the yolk globules 

 which are the first to become disturbed are also the first to redistril^ute 

 themselves. The substance of the gray-cap does not become rearranged 

 and probably takes no jDart in emlsryonic development. The vesicular 

 zone generally disappears in a short time. When it does not become re- 

 distributed an abnormal embryo develops leading one to conclude that 

 this substance is necessary for normal development. When no redistribu- 

 tion takes place in any of the zones a dwarf embryo is produced at the inner 

 end, that is, where the cytoplasm and nuclei have gathered. 



The age of the egg when centrifuged has a marked influence ujxjn its 

 later growth. The general statement may be -made that the older the egg 

 the more chances there are of its normal development after centrifuging. 

 A large number of experiments with beetles' eggs show that eggs in the 

 blastotlerm stage or older always produce normal embryos and sometimes 

 larvae. 



The rate of develo]Mnent is apparently not affected by centrifugal force. 

 The average ])eriod for the hatching of the eggs of C. multipunctata is five 

 and two-thirds days (Hegner, 1908). 



Several beetles were centrifuged and the eggs they laid carefully examined. 

 In the majority of cases the eggs showed no rearrangement of materials 

 and the production of embryoes and larvae was not impeded. In one case 

 however, two abnormal emliryoes developed from eggs which had been 

 centrifuged within the mother before the germinttl vesicles had broken 

 down. 



