64 THE FIRST PRINCIPLES OF HEREDITY 



hair, feathers, stripes, etc.) to the interaction and co- 

 operation of various cells. He admits some kind of organi- 

 zation for the germ-plasm ; though, as we shaU see later, he 

 lays considerable stress on the accompanying influences 

 between the cells themselves — i.e., forces external to, and 

 not originally residing in, the germ-plasm. 



The greatest objection against Weismann's teaching that 

 the formation of any part of an organism can be due only 

 to the presence of active specific determinants seems to 

 be furnished by those pathological cases where, after the 

 fracture of a bone, a false joint is formed, with proper 

 capsule, etc. Here we have only two alternatives : either 

 adventitious determinants are present in a latent state 

 wherever the formation of a false joint may happen to 

 occur — a very unlikely provision for pathological cases — 

 or a specific structure can be formed without such 

 determinants. 



We are, as can be seen, in the not very fortunate position, 

 pointed out at the beginning of the chapter, that not one 

 of the theories propounded is free from objections and 

 contradictions. Not a single theory can be made to fit in 

 with all known facts. On the whole, Weismann's theory 

 seems to give the most complete explanation, an explana- 

 tion to which in its fundamentals we must hold ourselves, 

 with more or less modifications, in the present state of our 

 knowledge. 



In the following paragraphs of this chapter and the next 

 we shall therefore mainly follow Weismann's detailed 

 statements, as at least offering a working model for picturing 

 to ourselves the intricate processes of inheritance. Of 

 other theories we shall mention only as much as appears 

 essential for the discussion. 



II.— THEORY OF MATURATION. 



We have seen that the germ-cells possess before matura- 

 tion the ordinary number of chromosomes typical of the 

 cells of the species, but that they lose in the process of 



