7O T. H. MORGAN. 



I 



egg during the segmentation stages and pregastrula stages is 

 equal to or greater than the space of the blastocoel. On account 

 of the variation in size of different eggs it would have been better 

 to measure the same egg at different times. I shall give some 

 measurements of several eggs of the same bunch but not the 

 same eggs. In one case the unsegmented eggs measured 5.1, 



5.2, 5.3 and 5.4. The average eggs seem about 5.3. At the 

 beginning of gastrulation the eggs measured 5.6 and 5.7. When 

 the dorsal lip was widely horseshoe-shaped the eggs measured 

 5.6 and 5.8 ; and when the gastrula lips were nearly close 5.8 

 and 5.9. In another case the unsegmented eggs measured 5.2, 



5.3, 5.4 and at the beginning of gastrulation 5.5, 5.6, 5.7. In 

 another case the unsegmented eggs measured 5.2, 5.3, 5.4, and at 

 the beginning of gastrulation 5.4, 5.5, 5.8. 



If we assume that the unsegmented egg measures 5.3 and 

 that the egg about to gastrulate measures 5.6, the latter will 

 have gained about two ninths of the volume of the former, 

 or roughly one fourth. An approximate estimate of the size 

 of the blastocoel when fully formed, as compared with the 

 blastula in which it is contained, shows that the blastocoel is 

 about one eighth the entire volume. Hence, while the egg has 

 gained one fourth in volume, only one eighth of its increase is 

 due to the segmentation cavity ; i. e., only one half of the in- 

 crease in size can be accounted for by the segmentation cavity 

 alone, and the other half must have been due to the absorption 

 of water by the cells of the blastula. Thus we must conclude 

 that the egg is absorbing water during the segmentation stages, 

 and that at the same time it is giving up to the blastocoel an 

 amount of fluid that is approximately half of the amount absorbed. 

 If the egg is placed under conditions where it can not absorb 

 water, it gives up, nevertheless, nearly the normal amount to the 

 blastoccjel. 



OBLITERATION OF THE BLASTOCCEL BY MEANS OF A CENTRIFU- 

 GAL FORCE AND THE EFFECT ON SUBSEQUENT DEVELOPMENT. 



The eggs of Rana sylvestris in a late blastula stage were put 

 into tubes of water and revolved on a small centrifuge at the rate 



o 



of i, 600 revolutions per minute for ten minutes. At the end of 



