364 THEOPHILUS S. PAINTEE 



chromatin. A typical case is shown in figure 15. Here there 

 are six cells besides the P2 and EMSt blastomeres. One of these 

 is evidently an enucleated protoplasmic ball, so characteristic 

 of the tetraster eggs. The remainder came from the division. 

 It will be noted that one of the small blastomeres contains a 

 large amount of waste chromatin. This is a very common 

 phenomenon exhibited by such eggs after division. In this egg, 

 we also see that the MSt blastomere is not dividing in the same 

 plane as the Po. Such a condition is seldom met with. 



The later development of these eggs which have had a tetraster 

 in the Si blastomere, is extremely abnormal. The Si derivatives 

 divide irregularly ; they become scattered over the surface of the 

 embryo or lie in one heap ; and there is every indication that they 

 very rarely or never form a cleavage cavity and gastrulate. In 

 later cleavage stages, the abnormalities caused by these tetraster 

 eggs is very striking. One of the marks of such eggs is the 

 presence of the small cell with the large amount of chromatin 

 (fig. 15). This disorganization, however, does not extend to the 

 primordial germ cell, for we find it dividing normally in later 

 stages when the embryo is otherwise totally abnormal. 



At the time of gastrulation, a majority of the embryos appear 

 normal or exhibit minor irregularities, such as a slight asym- 

 metry of shape. The cleavage cavity is present in such eggs, 

 however, and there seems to be no reason why they should not 

 gastrulate normally. Among such embryos one finds a large 

 number which have no cleavage cavity. This sometimes 

 appears to be due to the fact that the ectodermal cells are too 

 scattered or are too few in number to form it. But in every 

 case the primordial germ cell nuclei may be clearly seen. 



To sum up the foregoing description, we find that the abnormal 

 eggs are of three types: (a) Eggs in which the A and B blasto- 

 meres have abnormal positions in the 4-ceir and later stages, 

 (b) Eggs in which there has been an asymmetrical distribution 

 of the chromatin between the A and B cells, (c) Eggs with a 

 tetraster in the Si blastomere. We have now to inquire how 

 these three abnormal conditions arose from the eggs just re- 

 moved from the CO2. And, secondly, what relation these ab- 



