THE CYCLE OF LIFE 383 



stimulate the ovum to divide, or remove some embargo 

 which hinders the ovum from starting on its course of 

 development. It is possible that some ferment may be 

 introduced in ordinary fertilization, but the remarkable 

 experimental work of recent years shows that a great 

 variety of stimuli may serve to set the egg dividing. It 

 is difficult to discern what is the common feature in these 

 diverse trigger-pulling stimuli. 



Artificial Parthenogenesis. Our knowledge of the 

 very interesting phenomena commonly referred to as 

 artificial parthenogenesis is in great part due to two 

 experimenters of the first rank, Professor Jacques 

 Loeb and Professor Yves Delage. Loeb began by 

 showing that the action of the male element could be 

 facilitated or its range of possible action increased by 

 altering the conditions. In sea-water rendered faintly 

 alkaline the eggs of the sea-urchin could be fertilized 

 by the sperms of many different kinds of starfish, though 

 this did not occur in ordinary sea-water. But this was 

 but the beginning of his remarkable series of researches. 

 He put the eggs of the sea-urchin into sea-water to which 

 had been added a little formic, acetic, or butyric acid, 

 and then after a minute or two replaced them in normal 

 sea-water. They began to show the initial stages of nuclear 

 division. But when he transferred ova from the acidified 

 sea- water to more concentrated sea- water, to which common 

 salt had been added, they developed normally and at the 

 usual rate, and formed free-swimming larvae. Similar 

 experiments have been successfully made with several 

 kinds of worms and molluscs. 



Loeb, Delage, and others have shown in a considerable 

 variety of cases that artificial parthenogenesis can be 



