Centrifugal Force upon Beetles^ ^SS^ 549 



gtay cap at the outer end, and (3) a comparatively large intermedi- 

 ate mass of yolk, the larger globules lying at the outer end of this 

 layer. 



2 The gray cap is induced by a lesser amount of centrifugal 

 force in an egg containing many cleavage nuclei than in a fresh 

 egg. Either the gray cap material is liberated during development 

 or else some condition of the yolk mass in the older egg allovs^s 

 it to pass more rapidly tov^ard the heavier end. The gray cap 

 material is not necessary for the normal development of the 

 embryo. 



3 The vesicular zone becomes visible after fifteen minutes of 

 centrifuging. It is composed of fat imbedded in cytoplasm. 

 This zone disappears during development. 



4 The yolk globules are distributed throughout the inter- 

 mediate region of the egg; the largest spheres are at the outer 

 heavy end. It takes very little centrifugal force to cause this 

 rearrangement. Restitution to the normal condition takes place 

 soon after the egg is removed from the centrifugal machine. 



5 The cytoplasm is lighter than the gray cap material or the 

 yolk, but heavier than the fat of the vesicular zone. The passage 

 of the cytoplasm to the light end of the egg does not incapacitate 

 it for the production of an embryo. 



6 The nuclei are apparently equal in specific gravity to the 

 cytoplasm. Cleavage nuclei and vitellophags rise to the inner end 

 of the egg; the nuclei of the blastoderm of older eggs are not visibly 

 influenced by centrifugal force. 



7 The germ-cell determinants move en masse from their usual 

 position at the posterior end toward the anterior end when the 

 former is placed inward. The further history of these granules 

 has not been traced. 



8 Restitution takes place very slowly. Those substances 

 easily displaced are also the first to redistribute themselves. 

 The cytoplasm seldom regains its normal position, but produces a 

 dwarf embryo outside of the yolk at the light end of the egg. 



9 The age of the egg determines the susceptibility to centri- 

 fugal force and the future growth of the embryo. In general 

 an egg in a late cleavage stage becomes stratified sooner than a 



