46 



Life and Death, Heredity and Evolution 



details it seems extraordinary that anyone should doubt that 

 acquired characters are inherited. 



Let us examine first the simplest possible case, of an ac- 

 quired injury or mutilation. Suppose that in Difflugia one 

 or more of the spines is broken off, or a hole is broken in the 

 shell (Figure 14). Is there any reason why when this 

 animal reproduces, the progeny should have a corresponding 

 broken spine or broken shell? The offspring produces anew 



Figure 15. Reproduction in an infusorian (Paramecium) in which 

 the anterior end has been cut off. At the first division the posterior 

 offspring is quite normal, and by the third division even the anterior 

 offspring has regained its normal anterior tip. Only the divisions of 

 the mutilated individual are represented, as all others produce normal 

 offspring. After Jennings, 1908. 



its own shell and spines ; what sort it shall produce under 

 given outer conditions depends on the nature of its proto- 

 plasm and nucleus. These are not altered by the breaking 

 of the shell or spine of the parent, and as a matter of fact 

 we find that the offspring produce entire shells and spines, 

 just as their parents did. The injuries acquired by the 

 parent are not inherited. Again, look at an infusorian with 

 its anterior tip cut off (Figure 15). Is there any reason 

 why the offspring produced from the hinder half should have 

 its anterior tip cut off? As a matter of fact, it has not. 



