HEREDITY. THEORY OF WEISMANN. 2/1 



matical principle, when the body increases in size, 

 the surface increases as the square of the dimensions, 

 while the bulk increases as their cube. The bulk of 

 the animal increases, therefore, faster than the ab- 

 sorptive surface. The animal continues feeding and 

 growing, until it finally reaches a size when its bulk 

 is too great to be kept supplied with the nourish- 

 ment absorbed by its surface. When this limit is 

 reached, the body simply breaks into two pieces, 

 each of which becomes independent, and goes on 

 feeding precisely as did the original animal, until 

 once more the limit is reached. Here is a simple 

 form of heredity, and there is no difficulty in under- 

 standing it. Each of the resulting individuals is like 

 the other, and like the original, because each is half 

 of this original. And there is, therefore, no reason 

 why they should be unlike. Now, with this simple 

 case in our minds, it is not difficult to explain 

 heredity in higher animals. Every animal, let us 

 for convenience say man, is derived from an ovum, 

 which is, like the amoeba, a single cell composed of 

 a mass of protoplasm. Of course, this ovum differs 

 from the amoeba in possessing the power to develop 

 into a complicated man, but, nevertheless, it is a 

 single cell, and in this sense the two are strictly 

 comparable. When this ovum begins to develop 

 toward the adult, the first change that takes place is 

 its division into two parts. Now, remembering the 

 former case, Weismann says that, just as it was not 

 difficult to see how the two halves of the divided 

 amoeba were alike, so it is not difficult to understand 

 here how each half of the divided ovum is like the 



