340 EDWIN G. CONKLIN 



ever, the micromeres formed from each macromere are normal 

 in nmiiber and relative position as is best shown in figure 110. 

 In none of these eggs is there any evidence that the polarity or 

 pattern of organization has been changed in any quadrant, 

 though the relations of the different quadrants to one another is 

 changed. 



Ij.. Results of centrifuging during the third and fourth cleavages 

 {figs. 97 to 104, 113 to 122) 



Centrifuging during the third and fourth cleavages is of especial 

 interest because these cleavages are under normal conditions 

 plainly differential and lead to the formation of the first and sec- 

 ond groups of micromeres (ectomeres). In this case as in every 

 other one, the cytoplasm and yolk may be moved more easily 

 than the mitotic figure or the resting nucleus and centrospheres. 

 In figures 97 to 102 eggs are shown which were centrifuged dur- 

 ing the third cleavage mitosis; in figures 97 and 98 the axis of 

 centrifuging was at right angles to the egg axis and the fibers 

 connecting the upper pole of the spindles with the animal pole 

 are clearly shown in those cells in which yolk was forced to the 

 animal pole. A later condition of such an egg is shown in 

 figure 100, in which the micromeres Ic and Id were formed some 

 distance from the animal pole owing to the fact that yolk was 

 forced to that pole in the macromeres IC and ID. In figure 99 

 the axis of centrifuging was in the direction of the egg axis, 

 the animal pole being centrifuged in position; consequently 

 yolk was driven to the animal pole and cytoplasm to the vegetal 

 one. The further development of such an egg is shown in figures 

 101 and 102 in which the first set of micromeres {la-Id) are yolk 

 laden and much larger than normal. Figure 102 is especially 

 instructive because it shows the second set of micromeres {2a- 

 2d) being formed in a manner entirely normal in quadrants B 

 and C although the size and contents of the first set of micro- 

 meres {Ih, Ic) was very abnormal in these quadrants. Further- 

 more, the orientation of the spindles in the cells lb, Ic shows 

 that a small protoplasmic cell will be formed at the upper pole 

 of this spindle, a large yolk cell at the lower pole, which is just 



