MYSTEP.Y OF THE CELL 309 



fessor Thomson's very short summary of it, giving an explana- 

 tion of Weismann's special terminology. Weismann's state- 

 ment is as follows: 



" The germ-substance owes its marvellous power of development 

 not only to its chemico-physical constitution, but to the fact that it 

 consists of many different kinds of primary constituents, that is, 

 of groups of vital units equipped witli the forces of life, and capa- 

 ble of interposing actively and in a specific manner, but also 

 capable of remaining latent in a passive state until they are af- 

 fected by a liberating stimulus, and on this account able U) inter- 

 pose successfully in development. The germ-cell cannot be merely 

 a simple organism; it must be a fabric made up of many different 

 organisms or units — a microcosm." ^ 



And Professor J. A. Thomson's Summary of Weismann's 

 mechanics of the germ-plasm is as follows : 



Summary 



" The physical basis of inheritance — the germ-plasm — is in 

 the chromatin of the nucleus of the germ-cell. 



" The chromatin takes the form of a definite number of chromo- 

 somes or idants (Fig. 110, B, C, D, id). 



" The chromosomes consist of ids, each of which contains a 

 complete inheritance. 



" Each id consists of numerous primary constituents or deter- 

 minants. 



" A determinant is usually a group of hiophors, the minutest 

 vital units. 



" The biophor is an integrate of numerous chemical molecules." 



In the preceding Summary I have italicised the technical 

 terms invented by Weismann for the different stages of what 

 may be called the mechanical explanation of heredity by 

 means of the successive changes observed in the growing and 

 dividing germ-cells. But, as he himself admits, it explains 

 nothing Avithout taking for granted the essential phenomena of 

 life — nutrition, assimilation, and growth; and these are ad- 

 mitted to be to this day quite unexplainable. 



iThe Evolution Tlipory, trans, by J. A. Tlionison. 1004. vol. i. p. 402. 



