DEVELOPMENT OF PAEACOPIDOSOMOPSIS 15 



egg. The study of many two-celled stages reveals the fact that 

 the two blastomeres are not always of the same size. Their 

 disproportion in size may be accentuated by the position the 

 plastic egg happens to take on the slide. 



The nucleolus becomes associated with one of the daughter 

 nuclei (fig. 14), and is thus included in the blastomere formed 

 about that nucleus (fig. 15). It passes into the cell unchanged 

 (text fig. 1, A-H). 



b. The second division 



In preparation for the second division, each mitotic spindle 

 is arranged so that the angle formed by its major axis and the 

 long axis of the egg is less than a right angle, and with this axis 

 lying more or less parallel with the outside margin of the cell 

 (fig. 16 and text-fig. 1, F-H). WTien the divisions are com- 

 pleted, the four-celled stage consists of two cells forming the base 

 of the egg and two lying above these, one on each side (fig. 18 

 and text fig. 1, 1, J, K, 0). This is the typical arrangement; but 

 there are variations from this typical figure in which only one of 

 the blastomeres forms the base of the egg (text fig. 1, L, M, N, 

 P). Such variations may be due to one of two causes, either the 

 blastomeres shift after they are formed or, what is more probable, 

 the direction of the mitotic spindle in one or both blastomeres 

 varies from that seen in such figures as 16. 



The nucleolus, which, as we have seen, enters one of the first 

 two blastomeres, again passes unchanged into a single cell (text 

 fig. 1, /). The nucleolus is thus invariably inherited by one of 

 the first four blastomeres. Very shortly after the second division 

 is completed, this pecuhar body breaks up and forms a granular 

 area lying about one side of the nucleus (figs. 17, 18 and text 



fig. 1, J-P). 



It would be interesting to know whether it is always received 

 by a definite cell; that is to say, whether in all four-celled stages 

 the blastomeres inheriting the nucleolus are homologous. ^\Tiile 

 this point is difficult to determine, nevertheless, after examining 

 many two- and four-celled stages, I have reached the conclusion 

 that its distribution is a matter of chance. In the first place, if 



