PLATE 23 



EXPLANATION OF FIGURES 



119 to 122 (1151 and 1152) Centrifuged 5 hours in the 8-celI stage, fixed 5 

 hours later. In these eggs the animal pole was centrifugal in position, conse- 

 quently the cytoplasm and the nuclei of the macromeres, A, B, C, D, were forced 

 awaj; from the animal pole by the yolk and were held in this new position dur- 

 ing one or more cleavages. As a result the second set of micromeres {2a-2d) 

 are small protoplasmic cells at the vegetal pole (figs. 199, 121, 122) or they are 

 large yolk-rich cells at the upper pole (fig. 120). 



123 (1152) Centrifuged 5 hours in the 2-cell stage, fixed 5 hours later. The 

 second cleavage was forced to form in the equator of the egg, and the first set 

 of micromeres {la-Id) were cut off on one side of the animal pole and are larger 

 than normal. All the macromeres are dividing to form the second set of micro- 

 meres {2a-2d) which will lie on the animal pole side of those cells. Two cells 

 of the first set {la-Id) are dividing laeotropically as in normal eggs. 



124 (1154) Centrifuged 5 hours in the 8-cell stage in the direction shown 

 by the arrow ; fixed 24 hours later. The cytoplasm and the nuclei of the macro- 

 meres were thrown to the left and toward the vegetal pole and small cells were 

 cut ofT in this position. 



418 



