MICHIGAN ACADEMY OF SCIENCE. 51 



end (the heavy end) of each was touched with a hot needle. In this way 

 the gray-cap material was coagulated and hence prevented from taking 

 part in further development. 



All of the control eggs, that is the eggs that were centrifuged but were 

 not operated upon with the hot needle, hatched at the same time as those 

 that had not been centrifuged. In the eggs centrifuged with the anterior 

 end toward the center of rotation, the gray cap was thrown toward the 

 posterior end. Nine of these eggs were operated upon with the hot needle. 

 One of them hatched at the same time as did the control eggs; the other 

 eight developed up to the hatching stage but the larvae failed to emerge. 



In the eggs centrifuged with the posterior end toward the center of rota- 

 tion, the gray cap was thrown to the anterior end. Eight of these eggs 

 were operated upon with the hot needle. On the sixth day one of these 

 contained a larva ready to hatch but the other seven were apparently unde- 

 veloped. After these were prepared for microscopical examination each 

 egg exhibited a shapeless mass of tissue near the center, occupying about 

 one third of the total mass, whereas the rest of the egg substance consisted 

 of homogeneous yolk material. This result may have been due and prob- 

 ably was due to the effects of the centrifugal force rather than to the de- 

 struction of the gray-cap material. 



Conclusion. The results of these experiments lead to the conclusion that 

 the gray-cap material is not necessary for normal development and should 

 therefore not be regarded as an organ-forming substance except in so far 

 as it may furnish nutriment for the developing embryo. 



Experiments to determine whether the changes in the position of the egg sub- 

 stances affect the polarity of the egg. 



Experiment A. Sixteen eggs were placed in the centrifuge 18 hours after 

 their deposition and rotated for 20 hours. Eight of them were placed with 

 the anterior end and eight with the posterior end toward the center of rota- 

 tion. They were allowed to develop after their removal from the centri- 

 fuge. Shortly before hatching the orientation of the embryos was deter- 

 mined and in every case it had not been influenced by the centrifugal force. 

 All of the eggs hatched and apparent^ normal larvae emerged. 



Experiment B. This experiment was similar to Experiment A except that 

 the eggs were onlj- one hour old instead of 18 hours old and they were rotated 

 for twenty-two hours instead of twenty hours. Only four of the eight 

 eggs that were centrifuged with the posterior end toward the center of rota- 

 tion hatched. The orientation of these was not influenced by the centri- 

 fugal force. Seven of the eight eggs that were centrifuged with the anterior 

 end toward the center of rotation developed normally and hatched. The 

 orientation of these was likewise uninfluenced by the centrifugal force. In 

 both sets of eggs hatching was slightly delayed. 



Experiment C. Twenty eggs 19 hours old were centrifuged in various 

 positions for one and one-half hours. The orientation of the embrj^os was 

 not disturbed and all of them hatched in the normal period. 



Experiment D. Sixteen eggs four hours old were centrifuged slowh' until 

 they hatched, at the end of six days. Eight were placed with the anterior 

 end and eight with the posterior end toward the center of rotation. The 

 embryos all exhibited a normal orientation. 



Experiment E. This experiment was similar to Experiment D except that 

 the eggs were twenty-two hours old when rotation was begun and were 

 rotated much more rapidly. No larvae hatched from these eggs and the 

 embryos which developed in them differ from normal embrj'os in several 



