THE PHYSIOLOGY OF CELL DIVISION 27 



A corresponding reversibility in the associated permeability- 

 change is thus implied. Now, the initial cytolytic process 

 caused in sea-urchin eggs by fatty acids or other cytolytic sub- 

 stances appears to be imperfectly reversible unless the egg is 

 afterwards subjected to a second treatment, which consists in 

 exposure for a certain time to oxygen-containing hypertonic 

 sea-water (for twenty to thirty minutes at 20°), or to cold (for sev- 

 eral hours) or to cyanide-containing sea-water (for several hours) 

 Sea-urchin eggs subjected to a simple membrane-forming treat- 

 ment and then returned to sea-water typically undergo cytoly- 

 sis, usually after some irregular form-change with perhaps an 

 occasional cleavage. But after appropriate treatment with hy- 

 pertonic sea-water, cold, or cyanide, many of these eggs are re- 

 stored to an essentially normal state and proceed normally with 

 their development.^^ The necessity of such after-treatment, fol- 

 lowing the initial membranolytic or permeability-increasing pro- 

 cess appears, however, to vary widely in different eggs. Sea- 

 urchin eggs are characterized by a certain inertia or inability to 

 recover a normal condition without such supplementary treat- 

 ment. Starfish eggs, on the contrary, may develop normally in a 

 large proportion of cases after simple membrane-formation by 

 heat or fatty acid.^^ In other eggs a local mechanical irritation 

 may also be followed by normal development, as in Bataillon's 

 experiments with amphibian eggs.^'' In some of the experiments 

 described in the present paper the starfish eggs were found to 

 develop more favorably without the after-treatment with hyper- 

 tonic sea-water, cyanide, or anesthetics, than with it. In these 

 cases it is to be assumed that the egg spontaneously reverts to 

 the normal condition of semi-permeability, and hence is enabled 

 to proceed normally with its development. Such spontaneous 

 recovery of the normal properties after artificial membrane-forma- 

 tion rarely occurs with sea-urchin eggs, where the after-treatment 



" Cf. J. Loeb, loc. cit. 



^^ See below. Cf . also my earlier paper on parthenogenesis by temporary 

 warming, Journal of Experimental Zoology, 1908, vol. 5, p. 375. 



^^ Bataillon, Archives de Zoologie experimentale et generale, 1910, Ser. 5, vol. 

 6, p. 101. 



