358 THEOPHILUS S. PAINTER 



of such embryos. Typically they consist of a mass of cells, 

 among which one may distinguish the primordial germ cells, 

 but no organization exists and quite frequently it is evident that 

 no cleavage cavity was ever formed in the embryo, consequently, 

 that gastrulation had not taken place. 



Eggs preserved as they were taken from the ice chest, where 

 they had been since their removal from the CO2, showed a slight 

 amount of development. All of them had divided at least once, 

 and something less than half (227 out of 505 eggs counted) had 

 reached the 3-cell stage. Occasionally, in such a preparation, 

 a 4-cell stage is found. 



An examination of these 3-cell stages (fig. 1) shows that the 

 Si blastomere has divided to form the A and B cells, while the 

 Pi blastomere is in a 'resting stage.' The nuclear condition of the 

 A and B cells is normal: as may be seen by the figure, waste 

 chromatin occurs in one or both of the cells showing that the 

 diminution process has taken place, but the two cells do not 

 always lie pressed against each other as is normally the case 

 (compare fig. 1 with text fig. F). In 50 eggs out of 78, examined 

 at random for this point, the A and B blastomeres were separated, 

 in extreme cases the two cells lying on opposite sides of the Pi 

 cell. 



Among the eggs in the 2-cell stage, 101 out of 278 cases showed 

 the Si cell dividing, with the chromosomes in the equatorial 

 plate phase. The remainder showed resting nuclei in both the 

 Si and P] blastomeres. A close examination of the equatorial 

 plates in the dividing cells shows an abnormal condition of the 

 chromatin (figs. 2a to 2d). Figures 2b, 2c, and 2d are drawn 

 at a higher magnification. In practically every case (96 out of 

 101 eggs examined for the point) the chromosomes were found 

 fused together. This fusion seems to affect the ends principally 

 (figs. 2a, 2d) leaving the middle portion free, but in extreme 

 cases even the middle parts are involved and all four chromosomes 

 are clumped together into one mass (figs. 2b and 2c). One very 

 constant feature of this fusion is the formation of what appear 

 to be vacuoles in the fused ends. It is also to be noted that when 

 only the ends of the chromosomes are involved the middle 



