Il6 E. G. SPAULDING. 



Greeley ! found however that artificial parthenogenesis could 

 be produced in Asterias eggs by exposing the eggs to a tempera- 

 ture of i 7 C. and then allowing this to rise, keeping them in 

 the same sea water all the time. This can be explained as follows : 







A lowering of the temperature directly reduces the osmotic pres- 

 sure of both medium and egg, yet increases the surface tension. 

 A potential difference within the egg in the direction of tension- 

 pressure is thus created, the equalization of which necessitates a 

 loss of water. This view is confirmed by the spherical form as- 

 sumed and the losing of water by many species as a result of 

 exposure to low temperatures. 2 The loss of water as a result of 

 the increased contracting forces cannot continue indefinitely for 

 the reason that, by virtue of the increased osmotic pressure 

 caused by it, the egg itself would tend to absorb water. Con- 

 sequently the three processes must be considered to occur until 

 there is equilibrium in the entire "system" of egg-medium ; like- 

 wise they would continue to take place, though in opposite direc- 

 tions, when the temperature was subsequently raised; i. i\, the 

 pressure and tension would then both simultaneously decrease 

 and the egg absorb water. Consequently this method would 

 agree with our theoretical demand, that the event of cleavage is 

 always identical with a decrease in surface tension. 



(c) Electrical CJianges. 



The third possible way of bringing about changes in the egg 

 which are in themselves physical (electrical), but perhaps due 

 directly to chemical causes as we have indicated, is by the use 

 of electrolytic methods. These changes may have to do with 

 both pressure and tension at the same time and we have referred 

 to them previously as perhaps to. be necessarily considered as 

 present in any case in order to account for the constricted 

 form of cleavage. For it can be shown that every method that 

 we have analyzed may, at the same time that it results in the 

 changes in chemical composition, pressure and tension, have 

 also accompanying these a change in the electrical condition of 

 the egg. 



1 Am. Journal of Physiology, ^ 7 I., 1902, p. 296. 



2 Greeley, Am. Journal of Physiology, 1901, VI., p. 122; BIOLOGICAL BUL- 

 LETIN, III., p. 165 and V., p. 42. 



