FROM THE TWO-CELLED STAGE ONWARDS. 



3' 



VIII. FROM THE TWO-CELL STAGE ONWARDS. 



After completion of the first cleavage each of the two resulting cells or blastomeres passes through a series of 

 chano-es analogous to those occurring in the undivided egg after the union of the germ-nuclei. In the first place 

 the nucleus greatly enlarges and its staining power gradually increases. In the second place the horseshoe-shaped 

 aster (cf. Figs. XIX. and XII. A) divides into two halves which place themselves at opposite poles of the nucleus, 

 90° away from the centre of the mother-aster. The astral rays meanwhile become shorter, and the centre of each 

 aster ao-ain acquires the capacity of staining light red after double staining with hzematoxylin and Congo red, while 

 the rays are blue. 



The subsequent stages repeat those already described in the undivided egg without essential modification. 



\ 



\ 





s &i 



■/:>IS>: 



X/ 



..-'-^.- 



^^i^:^ 





^ 



\ 



/ 



Fig. XX. 



Fig. XX. — Two-celled stage during the "pause" or resting-stage. 

 The nuclei have greatlv increaseil in size and staining power, and contain many chromatic rings liesides the reticulum. The aster has completely divided, forming two asters in each cell. 



(Cf. Fig. XIII. A.) (Phototype 37.) 



Plate X. Phototype 37. 



Two-cell Slao-e durino- the Pause. 



The mother-aster has divided into two in each cell, and the nuclei have considerably increased in size and staining 

 power. The position of the asters shows that the plane of the second cleavage, at right angles to the first, is fully 

 predetermined. No trace of the mid-body remains, and the former spindle has been entirely resolved into cytoplasm. 



Plate X. Phototype 38. 



Two-cell Siage preparing for the Second Cleavage. 



A t3'pical karyokinetic figure is forming in each cell at right angles to that of the first cleavage. 



