The Mechanistic Conception of Life 



worms, or even birds, show a tendency to a nuclear or even a 

 cell division; and R. Hertwig, Mead, and Morgan had suc- 

 ceeded in inducing one or more cell divisions artificially in 

 such eggs. But the cell divisions in these cases never led 

 to the development of a larva, but at the best to the formation 

 of an abnormal mass of cells which soon perished. 



I succeeded twelve years ago in causing the unfertilized 

 eggs of the sea-urchin to develop into swimming larvae by 

 treating them with sea-water, the concentration of which was 



Fig. 1 



Fig. 2 



Fig. 1. — Unfertilized egg of the sea-urchin surrounded by spermatozoa. Only 

 the heads of the spermatozoa are drawn, since at the magnification used the tails 

 were not visible. 



Fig. 2. — The same egg immediately after the entrance of the spermatozoon. 

 The egg is surrounded by a larger circle, the fertilization membrane, which is 

 formed through the action of the spermatozoon. This formation of a fertilization 

 membrane can be induced by a pm-ely chemical treatment of the egg. 



raised through the addition of a small but definite quantity 

 of a salt or sugar. The eggs were put for two hours into a 

 solution the osmotic pressure of which had been raised to a 

 certain height. When the eggs were put back into normal 

 sea-water they developed into larvae and a part of these 

 larvae formed an intestine and a skeleton. The same result 

 was obtained in the eggs of other animals, star-fish, worms, 

 and mollusks. These experiments proved the possibility 

 of substituting physico-chemical agencies for the action of 

 the living spermatozoon, but did not yet explain how the 

 spermatozoon causes the development of the egg, since m 



