TEMPERATURE AND ARTIFICIAL PARTHENOGENESIS. 135 



exists in a very delicate condition of equilibrium as regards its 

 relation to the surrounding temperature. An increase in tem- 

 perature of only 3 C. over that of the room (24 C. to 27 C.) 

 suffices to liquefy the protoplasm of the egg. Within two hours 

 after the eggs have been exposed to this increase in temperature, 

 the protoplasm loses its granular appearance, becomes clear and 

 homogeneous and flows out, greatly extending the egg membrane. 

 At the same time or before the process of liquefaction has be- 

 come complete, the nuclear wall breaks down or goes into solu- 

 tion, and the eggs in this stage appear to contain from two to 

 thirty or more nuclear fragments scattered throughout the cell. 

 After six to eight hours' exposure to this increase in temperature, 

 the protoplasm goes into heat-rigor, but beyond the fragmenta- 

 tion of the nucleus, in no case was there even a semblance of 



segmentation. 



This exceedingly delicate condition of equilibrium as regards the 

 physical condition of the protoplasm of the unfertilized Asterias 

 egg and its relation to the surrounding temperature, makes it so 

 sensitive to any increase in the temperature, that is seems well- 

 nigh impossible to cause the segmentation of the egg by that 

 means. 1 The subject is by no means closed, however, and fur- 

 ther experiments will be performed along this line. 



This profound change in the physical condition of the proto- 

 plasm as a result of a very slight increase of temperature may 

 explain the fact noted in all the descriptions of the experiments 

 in this paper, that at a temperature of 30 C., artificial parthen- 

 ogenesis cannot be produced with any of the methods hereto- 

 fore used. Even at a temperature of 27 C. the protoplasm of 

 the Asterias egg becomes completely liquefied, and in this con- 

 dition no segmentation of the egg can occur. 



SUMMARY. 



i. The length of exposure to a solution necessary to produce 

 artificial parthenogenesis of the unfertilized eggs of Asterias and 

 Arbacia varies inversely with the temperature. This applies to 



1 In a recent paper, however, Delage (Archives de Zool. Exper., 1902) describes 

 experiments in which he obtained artificial parthenogenesis of the Asterias egg by 

 raising the temperature. 



