64 CHARLES PACKARD. 



normal. It is abnormal only when the egg has been radiated so 

 long that the protoplasm has been injured. But if the radiation 

 is for periods up to 50 minutes, the polar bodies are well formed 

 and the remaining chromosomes appear to be normal until they 

 grow into the vesicular condition. The altered mode of develop- 

 ment in such cases has already been described. If the radiation 

 is short, that is, from 20 to 30 minutes, the chromatin does not 

 show evidences of injury until the time of cleavage. Since chro- 

 matin grows by taking up substances from the protoplasm it is 

 evident that the radiations have acted so as to interrupt this proc- 

 ess, probably by altering the chemical constitution of the chro- 

 matin. 



The unusual movement of the nucleus in radiated eggs calls 

 for further comment. After short exposures the nucleus moves 

 in a normal manner to a point slightly above the center of the egg 

 where it fuses with the sperm nucleus. But as the duration of 

 the exposure is lengthened it shows a greater and greater tendency 

 to remain at the pole. In every case it makes some attempt to 

 migrate inward, but its freedom of movement appears to be 

 inhibited by the peculiar attachment to the second polar body. 

 In many instances, especially in eggs radiated for 35 minutes or 

 more, this curious attachment is not found, the nucleus lying free 

 in the protoplasm. Following the extrusion of the second polar 

 body, a process which is normal in all respects, the remaining 

 chromosomes become vesicular and finally fuse to form a single 

 large vesicle, which, instead of moving toward the sperm nucleus, 

 remains in place. The chromatin which in the course of normal 

 development condenses into chromosomes after the two nuclei 

 have fused here develops into irregular masses, some of which 

 may migrate slightly; the greater number do not. That chro- 

 matin which moves furthest from the pole is most normal in 

 appearance. 



Why does the egg nucleus fail to travel toward the center of the 

 egg? The egg protoplasm has not been visibly injured ; indeed it 

 appears to be perfectly normal for it can draw in the sperm and 

 the latter moves at the usual rate up to the center of the egg. In 

 both monospermic and polyspermic eggs there is evidence that 

 extensive protoplasmic movements are taking place for the yolk 



