Centrifugal Force upon Beetles^ ^SS^ 547 



short lime (C.B. 5, c, and C.B. 2, c) ; in other cases it is still present 

 after sixty-five hours (C.B. 9, d. Fig. 16). The cytoplasm under- 

 goes a partial restitution, but in those cases where most of it has 

 accumulated in the inner region the embryo is formed at this place 

 (Figs. 16, 21, 22 and 23). 



5 The A ge of the Egg luhen Centrifuged 



The general statement may be made that the older the egg the 

 more chances there are of its normal development after centrifug- 

 ing. Morgan ('02, p. 265) states that the eggs of frogs "which have 

 divided once or twice will withstand a greater rate of revolution 

 than those that have not divided. Moreover, eggs that have seg- 

 mented a number of times, so that the content is divided by cell 

 walls, will develop normally at rates of revolution that kill or pro- 

 duce abnormalities in unsegmented eggs, or eggs just beginning 10 

 segment." The age of the egg also determines to a certain extent 

 the amount of stratification. In the eggs of Chretopterus (Lillie 

 '06, p. 184) the stratification is not so pronounced before the break- 

 ing down of the germinal vesicle and there is no gray cap formed. 

 Lyon ('07, p. 168) could not distinguish any layers in unmatured 

 eggs of Asterias. 



The beetle's egg becomes stratified more quickly if centrifuged 

 when in a late cleavage stage than when fresh (compare C.B. 4, 

 d, Fig. 10, and C.B. 2, h, Fig. 18). Eggs that have reached the 

 blastoderm stage are more difficult to influence (C.B. 5, a, Fig. 

 19). The experiments described in this paper show that eggs 

 in the blastoderm stage or older almost always produce normal 

 embryos and some times larvae (C.B. 2, c; C.B. 2, d; C.B. 5, c; 

 C.B. 5, d; C.L. h, 3; C.L. s, 2; C.L.k. 2; L.D.k. 5; L.D. n, 6; 

 L.D. «, 7). 



/j. The Rate of Development 



The effect of agitation upon the rate of development is not cer- 

 tain because in several of the experiments reported the tempera- 

 ture was not carefully regulated. Meltzer ('03, p. 250) spates that 

 the eggs of the sea-urchin, Arbacia, develop into an advanced 

 cleavage stage more quickly than normally if they are violently 



