ILLUSTRATED AMONG PROTOZOA. 113 



caused by this constant and severe stimulus, we 

 may suppose the organism to have extended itself 

 to the utmost in different directions, — for the less 

 spherical its shape, the greater its relative sur- 

 face, — until finally the protoplasm parted and seg- 

 regated in two masses. This is the first step in 

 the multiplication of individuals. The two masses 

 of protoplasm are each of the same size, we will 

 suppose, as was the original mass at the beginning 

 of its existence. They are each, in the moment 

 when they come into existence, subjected to the 

 same permanent stimuli of the environment as acted 

 upon the parent at the beginning of its existence. 

 Also the occasional and periodic stimuli act upon 

 them in the same manner as they acted upon the 

 parent. Therefore, as a result of this similarity of 

 conditions, the two organisms naturally follow the 

 same course of development that was followed by 

 the parent organism. But there is this difference 

 between the parent and progeny : the two of the 

 latter generation are, at the first moment of their 

 existence, composed of protoplasm that has already 

 reacted many times to all the stimuli that affect it. 

 Once before it has been of the same size, and has 

 responded to the same constant and periodic stimuli 

 that affect it now. As those stimuli determined its 

 growth then, so they determine it now. Owing to 



