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 shail start by recounting experiments on the eggs of 
the Californian starfish Asterina,’ 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. 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 aspermatozoon. 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, 
1 Loeb, ‘Artificial Membrane Formation and Chemical Fertilization in a 
Starfish (Asterina),’’ University of California Publications, Physiology, II, 147, 
1905; Untersuchungen, p. 349. 
