PLATE 20 



EXPLANATION OF FIGURES 



101 (1038) Centrifuged 10 minutes during third cleavage, fixed 3 hours 

 later. Large yolk-laden micromeres were formed at the animal pole. 



102 (1035) Centrifuged 5 hour during third cleavage, fixed 3 hours later. 

 Egg essentially like the preceding. The micromeres of the first quartet, two of 

 which are dividing, are large and full of yolk, the micromeres of the second 

 quartet contain no yolk and are of normal size and constitution. 



103 (1050) Centrifuged 15 minutes, fixed at once. Centrifuged after the 

 formation of the first quartet of micromeres which are not displaced from the 

 animal pole, though the nuclei and centrospheres are displaced in these cells 

 in the same direction as in the macromeres. 



104 (1136, 4) Centrifuged 30 minutes during the second cleavage, fixed 12 

 hours later. The left half of the egg has developed normally, giving rise to two 

 macromeres, and each of these to three micromeres, two of which have subdi- 

 vided; the right half has divided into a large protoplasmic cell at the animal 

 pole and beneath this a yolk-rich cell which contains two large nuclei connected 

 by a chromatic thread, and four or more centrosomes and spheres, but the cell 

 has not divided. 



105 (1139, 2) Centrifuged 2| hours during the maturation division (?), 

 fixed 18 hours later. Both polar bodies, one of them large and containing a 

 spindle, lie at the pole opposite the protoplasmic cells, which is probably the 

 vegetal pole. The probable identity of the cell is indicated by the labelling and 

 the arrows, but the entire egg is abnormal and hard to interpret. 



106 (1129, 1) Centrifuged 10 minutes in gum arable, fixed 4 hours later. 

 Two eggs fused in the plane of the broken line, each in the 8-cell stage. The 

 polarity of each egg is unchanged by the fusion, asisshownby the positions of the 

 cells relative to the polar bodies. 



412 



