FIRST PERIOD OF DEVELOPMENT. 49 



The opening of the segmentation-cavity on both 

 sides is still wider than in the preceding stage 

 (Fig. 9). 



On observing this stage from the upper pole we 

 are struck by the beautiful regularity with which 

 these cells are arranged in two tiers. So far as 

 the activity and order of the cells are concerned 

 only one chief axis can be distinguished, which 

 reaches from the upper to the lower pole. The 

 polar body however is attached to a single upper cell. 



THIRTY-TWO CELLED STAOE (Fias. 10, 11). 



At the end of the next half-hour, i.e. three hours 

 after the liberation of the eggs, follows the further 

 division of all sixteen cells together, so that we 

 reach the stage with thirty-two cells. This means 

 that the eight upper as also the eight lower cells are 

 all divided simultaneously by means of furrows 

 running equatorially, and each one into two parts. 



Of the thirty-two cells which thus result the 

 eight situated at the lower pole are considerably 

 larger than the rest. Towards the upper pole, the 

 size gradually diminishes in the three further tiers 



E 



