HEREDITY. THEORY OF WEISMANN. 2/3 



is like the preceding generation. This is heredity 

 according to Weismann. A child does not inherit 

 any thing from its parents directly, but only from 

 the ovum. It is like its parents not because it has 

 inherited any thing from them, but because both 

 itself and its parents are derived from half of the 

 same ovum, an ovum existing in the body of its 

 grandparent. 



This is of course all hypothesis ; but it is very 

 simple, and has in its favor certain embryological 

 facts. But it will be seen that it absolutely pre- 

 cludes the possibility of any animal inheriting any 

 thing directly from its parents, and consequently 

 acquired variations cannot be transmitted to suc- 

 ceeding generations. According to this view, every 

 child would inherit exactly the same peculiarities 

 which its parents inherited, without reference to 

 any features which were developed in its parents by 

 mutilation, or use and disuse. Such acquired vari- 

 ations would only affect the adult and not the 

 ovum, and since the child inherits from the ovum 

 only they could not be inherited. Weismann ac- 

 cepts this conclusion, and goes to some length to 

 show that there is really no evidence that acquired 

 variations are inherited. He says that the only 

 variations which can be inherited are variations 

 which affect the ovum. If this should vary from 

 any cause, all individuals arising from it would of 

 course show the same results of the variation, and 

 since all future individuals do arise from this ovum, 

 by repeated division, it is evident that the results 

 of an ovum variation would affect all future genera- 



