360 THEOPHILUS S. PAINTEE 



unequal distribution of the chromatin). Here we fail to find 

 the usual waste chromatin in either the A or B cell. On the 

 other hand, one of the cells in such eggs always contains a very 

 large amount of deeply-staining reticular chromatin (fig. 6) 

 while its mate lacks this. This is a very constant feature of eggs 

 in which there has been an unequal distribution of the chromatin 

 between the A and B blastomeres. 



Among the 3-cell stages there is always a certain proportion 

 of eggs which are perfectly normal, as far as can be determined. 

 The Si cell is divided, the blastomeres lie pressed up against 

 each other, and the waste chromatin lying in the cyto- 

 plasm of these cells indicates that diminution has taken place. 

 There is a second type of 3-cell stage which is very striking 

 (figs. 7 and 8). In the egg shown in figure 7, the P2 and the 

 EMSt blastomeres have separated — are in a stage of division, in 

 fact while the Si cell is undivided and contains a tetraster. 

 Figure 8 shows the same condition of the Si cell and in addition 

 we note the enucleated protoplasmic ball lying on top of it. 

 Eggs showing tetrasters usually, if not always, possess this pro- 

 toplasmic ball. In figure 7 it is present, but lies under the other 

 cells and is not shown in the drawing. The amount of chro- 

 matin between the four centrosomes of the Si cell is very large. 

 It may be undergoing diminution or we may find the elongated 

 chromosomes still present. In the latter case, one may usually 

 count eight chromosomes lying in the spindles. In text figure D, 

 an egg is shown with a history similar to that of the tetraster 

 eggs, but for some reason, the centrosomes have failed to divide. 

 In this respect it is exceptional, but eight chromosomes and the 

 characteristic protoplasmic ball are both clearly seen. 



The 2-cell stages usually show the Si and the Pi blastomeres 

 undergoing division (fig. 9). Except for the axes of division, 

 which frequently do not occupy normal planes with regard to 

 each other, the division figures are typical of the untreated eggs; 

 and the lumpy condition of the chromatin of the Si cell, which 

 precedes diminution, is seen. 



A number of smears of eggs were preserved when the embryos 

 were in or just beyond the 4-cell stage, and in these, we find a 



