338 CHARLES PACKARD 



depending on the number of divisions of the first polar chromo- 

 somes, now migrate, still distinct, to the center of the egg, or 

 they may grow in size until they finally fill a large portion of the 

 egg. The latter condition is seen in figure 13. In the former 

 case (and such instances are rare) the egg divides abnormally. 

 The chromosomal vesicles become arranged on the cleavage 

 spindle and are unequally divided in the two daughter cells. 

 The larger number stays in the larger blastomere. The asters 

 are very slightly developed, but the spindle fibers and interzonal 

 fibers are very obvious; figure 14 shows this point. The total 

 number of vesicles remaining in the larger blastomere is about 

 28, and in the smaller, about 14. Whether these numbers are 

 significant or only accidental cannot be said since there are so 

 few cases of this phenomenon. 



Many of these eggs extrude no polar body at all. In such 

 instances the chromosomal vesicles fuse together and the karyo- 

 meres spin out into a spireme somewhat similar to that seen in 

 normal eggs immediately after the germ nuclei have fused. 

 But in these nuclei there is no nuclear wall (fig. 15) the chro- 

 mosome lying in a vacuole filled with a very faintly staining 

 substance. 



These observations point to the conclusion that cells may be 

 stimulated or retarded without suffering any marked morpho- 

 logical injuries. The effect has been physiological since only the 

 rate of metabolism has been affected. But with more severe 

 radiation the retardation is not so apparent because the embryos 

 die before developing far. A comparison of the injuries brought 

 about by the slow and rapid beta rays acting together with those 

 induced by the rapid rays alone reveals the curious fact that the 

 more intense radiation occasions less apparent disturbances. 

 This phenomenon superficially resembles that described by 

 Hertwig, who found that when the unfertilized frog egg is 

 radiated intensely, development after insemination is more 

 normal than when it is radiated more moderately. His ex- 

 planation is that the egg nucleus has been entirely inhibited from 

 taking part in cell division, so that only the normal sperm nucleus 

 divides. But in Nereis development after intense radiation is 



