PLATE 18 



EXPLANATION OP FIGURES 



Figure 89 is described on p. 420. 



90 (1071) Centrifuged 100 turns of hand machine at 2-celI stage, fixed at 

 once. Centrospheres lie between nuclei and animal pole, with which they are 

 connected by strands of cytoplasm. 



91 (1078) Two-cell stage centrifuged 100 turns of hand machine, fixed at 

 once. Axis of centrifuging oblique to egg axis. Centrospheres lie between 

 nuclei and polar bodies. 



92 (1148) Centrifuged 4 hours during first cleavage, fixed 18 hours later. 

 Development has been arrested. Cytoplasm, nuclei and centrospheres were 

 displaced toward the vegetal pole. The cleavage furrow has cut in from this 

 pole, leaving one centrosphere in one cell and both nuclei and the other centro- 

 sphere in the other cell. 



93, 94 (1158) Centrifuged 5 minutes during first cleavage, fixed 3 hours 

 later. Both first and second cleavage mitoses have taken place, but neither 

 cleavage furrow has formed in figure 93, and only one of them in figure 94. The 

 daughter nuclei show traces of division into gonomeres (male and female halves). 



408 



