240 



THE CELL 



As long as the eggs are under the influence of the cold, the 

 nuclear figures remain in this condition; however, the rigidity 



n 







FIG. 128. A Nuclear figure of an egg of 

 Strongylocentrotus, one hour and twenty minutes 

 after fertilisation. B Nuclear figure of an egg 

 of Strongyloceiitrotus; this was killed after hav- 

 ing been kept f&r two hours and fifteen minutes 

 in a freezing mixture, with a temperature of 

 - 2", in which it was placed one and a half houi 8 

 after the occurrence of fertilisation. 



gradually disappears when 

 the eggs are placed in a 

 drop of water upon an ob- 

 ject glass, and gradually 

 warmed up to the tempei-a- 

 ture of the room. After 5 

 or 10 minutes the two polar 

 radiations develop again at 

 the same places as before,, 

 at first being only faintly 

 seen, but finally being as 

 distinct as ever ; the spindle 

 threads reappear between, 

 the two poles, and division 

 proceeds in. the usual man- 

 ner. In such cases the cold 

 has acted only as a check, 

 the process of division sim- 

 ply going on from the point 

 at which it was arrested by the cold. 



A greater effect is produced if the eggs are subjected for about 

 2 to 3 hours to a temperature of from 2 to 3 Celsius below zero. 

 The whole nuclear figure is then fundamentally altered, and hence,, 

 when the cold rigor is over, it is obliged to reconstruct itself en- 

 tirely, on which account a longer period of recuperation is neces- 

 sary. The nuclear segments either become fused together to form 

 an irregularly-lobulated body, or they develop into a small vesi- 

 cular nucleus, such as is formed during the reconstruction process, 

 after division. Then changes begin anew, which result in the for- 

 mation of polar radiations, and frequentlyjof more or less abnormal 

 nuclear division figures. In fact the division of the egg-body is 

 not only considerably delayed, but even pathologically altered. 



Similarly certain chemical substances exert a marked effect 

 upon the process of division ('05 solution of sulphate of quinine 

 and 5 per cent, chloral hydrate). If eggs which have developed 

 spindles, and which exhibit the equatorial arrangement of the nu- 

 clear segments, are subjected for about 5 to 10 minutes to the 

 action of the above-mentioned substances, the pole radiations soon 

 commence to disappear completely. However, after a short period of 



