250 ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 



We have seen that the spermatozoon of any species has 

 substances which are able to call forth the development of the 

 sea-urchin egg. It harmonizes with this fact that the methods 

 of artificial parthenogenesis which are effective in the sea-urchin 

 must also be effective in other forms; although we must not 

 forget that the substances used in artificial parthenogenesis 

 are analogous in their effects but not necessarily identical with 

 those contained in the spermatozoon. This explains why in 

 each form quantitative modifications of the general method 

 are required. 



We shall start by recounting experiments on the eggs of 

 the Calif ornian starfish Asterina, 1 the eggs of which form a 

 splendid fertilization membrane after the entrance of a sperma- 

 tozoon. 



It was found at once that the formation of this membrane 

 can be induced by the same agents in the case of the eggs of 

 Asterina as in those of the sea-urchin; but there is a difference 

 in the concentration of the substances required. 



When the mature eggs of Asterina are placed in 50 c.c. of 

 sea-water in which 1 c.c. of benzol or amylene has been shaken 

 up, they all immediately form membranes that are indistin- 

 guishable in appearance from those formed after the entrance 

 of a spermatozoon. If the eggs are not removed from the benzol 

 or amylene sea-water immediately after membrane formation, 

 they succumb to cytolysis. 



If one of the lower fatty acids is used instead of the hydro- 

 carbon, no membranes are formed so long as the Asterina eggs 

 remain in the acidified sea-water; but a membrane is formed 

 at once after the eggs have been transferred to ordinary sea- 

 water, provided that the time of exposure to the acid has been 

 correctly chosen. Thus, if the eggs are placed for two minutes 

 in a mixture of 50 c.c. of sea-water +5 c.c. N/10 acetic acid, 



i Loeb, "Artificial Membrane Formation and Chemical Fertilization in a 

 Starfish (Asterina)," University of California Publications, Physiology, II, 147, 

 1905; Untersuchungen, p. 349. 



