PLATE 13 



EXPLANATION OF FIGURES 



Figure 65 is described on p. 410. 



66 (1040) Centrifuged 10 minutes, fixed 5 hours later. The first cleavage 

 spindle has been turned into the polar axis and the cleavage furrow is appear- 

 ing in an equatorial position. The animal pole is marked by the polar bodies, the 

 vegetal pole by the yolk lobe (yl). Development delayed about three hours. 



67 to 70, 72 (1035) Centrifuged 30 minutes, fixed 3 hours later. First cleav- 

 age equatorial. After centrifuging, the cytoplasm, nuclei and centrospheres in 

 the lower cells move as near as possible to the animal pole. One end of the 

 cleavage spindle remains near the animal pole, to which it is probably attached. 

 In figure 70 the centrosome which remained near the animal pole was separated 

 from its nucleus and has divided twice; the chromosomes and a portion of the 

 cytoplasm in the upper cell lie near the equator adjoining the cytoplasm and 

 spindle in the lower cell; the polarity is modified to this extent. In figure 72 

 the second cleavage is beginning in a meridional axis and nearly at right angles 

 to the first (equatorial) cleavage (1). 



398 



