HEREDITY i6i 



spermatozoon or the ovum ? Not at all. That which 

 is essential is that the spermatozoon or the ovum 

 should constitute foci of influences or impulses 

 proceeding from every tissue, and representing each 

 not only specifically, but in extent, in shape, in actual 

 condition. It is clear that the shape and conformation 

 of, let us say, the nose, the brow, the chin, could not 

 by any possibility be transmitted from parent to child 

 unless the force by which this is brought about 

 corresponded to each of these parts, not specifically, 

 but absolutely. In other words, the various cells of 

 which the nose, the brow, and the chin, are composed 

 are represented in the spermatozoon not as single 

 types of cells, but as collections of individual cells. 

 Only by force — and in this case by physiological force 

 corresponding exactly to the mould in which it is 

 generated — is it possible to produce or reproduce 

 shape. This is the bed-rock on which the dynamic 

 theory of heredity rests. 



Attention has been drawn to the fact that the The trans- 



znissioa of 



motor nerves are essentially nerves of chemical action, the in- 

 and in this respect all other nerves may be said to regional 

 resemble them to a greater or less extent by reason of ment""^' 

 the metabolism which constitutes an essential part of thenervous 

 their environment, both when functionally active and thftestis 

 when at rest. But whether the control which the *"^ °''^y- 

 nervous system exercises on metabolism is chiefly 

 through the sensory nerves and cells, or chiefly 

 through the motor nerves and cells, or through a 

 combination of the two, it is difficult to say, though 



11 



