WEISMANN'S THEORY OF HEREDITY 65 



This problem Weismann solved by analys- 

 ing the methods of reproduction among ani- 

 mals. These generally speaking are two; sex- 

 ual, and non-sexual or, as it is sometimes 

 termed, a-sexual. This latter form is the mode 

 that prevails at the bottom of the organic 

 scale — among the protozoa, animals con- 

 sisting of a single cell. This method has a 

 variety of forms v^hich are classified by Hae- 

 ckel as (i) self-division; (2) formation of 

 buds; (3) the formation of germ-cells or 

 spores. We shall here deal only with the first, 

 self-division, or fission, which is the most uni- 

 versal of all methods of propagation, being 

 the progress by which the individual cells 

 which compose all the higher animals multi- 

 ply themselves. This is the method vital to 

 Weismann's theory and the other two are no 

 more than distinct modifications of fission. 



When a Moneron or an Amoeba reaches a 

 certain size, it begins to pinch in the middle 

 like a tightly-laced corset. This increases until 

 the creature divides into two equal halves. 

 Each of these halves becomes a complete in- 

 dividual which continues to thrive until the 

 next division takes place. 



What Weismann observed as the most sign- 

 ificant thing about this was that in this pro- 

 cess and among these unicellular (single 



