• EFFECTS OF CARBON DIOXIDE ON EGGS 361 



trenieiidous variation in the relative proportions in which the 

 various abnormaUties described above occur. In one preparation 

 over 50 per cent of the eggs showed a tetraster in the Si blasto- 

 mere, or showed the later effects of it. In other slides only a 

 very small proportion of the eggs showed this abnormality. 

 The proportion of the eggs which showed an unequal distribution 

 of the chromatin between the A and B blastomeres, showed the 

 same variation in different slides. On the other hand, the fail- 

 ure of the blastomeres to form the rhombus is an abnormality 

 found in a large per cent of cases on every slide. 



Text figure D. 



In the large amount of material which was preserved at fre- 

 quent intervals after the 4-cell period, it has been possible to 

 follow the results of the abnormal conditions described through 

 the later development. Of course, as cleavage progresses, it 

 becomes increasingly difficult to follow the course of the indi- 

 vidual blastomeres, except in the case of the primordial germ 

 cell. The latter is usually conspicuous on account of the large 

 size of the nucleus. An analysis of the later stages has been 

 facilitated by the use of clay models of the eggs and a com- 

 parison of these with the excellent figures given by Boveri ('99). 

 In this way it has been possible to determine very exactly the 

 plane in which a given cell is dividing, and the relation it will 

 have to the rest of the blastomeres. 



