152 THE EVOLUTION THEORY 



visible increase so that the cell looks red. If there had previously 

 been no red granules present, thej^ might have arisen thi-ough the 

 breaking up of certain other particles — of protoplasm, for instance, in 

 the course of metabolism, so that, among other substances, red 

 granules of uric acid or some other red stuff' were produced. In 

 this case also the qualitative change would depend on an increase 

 or decrease of certain simpler molecules and atoms constituting the 

 protoplasm-molecule. Thus, in ultimate instance, all variations depend 

 upon quantitative changes of the constituents of which the varj'ing 

 part is composed. 



It might be objected to this argument that chemistry has made 

 us acquainted with isomeric combinations whose qualitative differences 

 do not depend upon a different number of the molecules composing 

 them, but upon their different arrangement ; it might be supposed 

 that something similar would occur also in morjohological relations. 

 And, in point of fact, this seems to be the case. We may, for instance, 

 imagine one hundred hairs as being at one time equally distributed 

 on the back of a beetle, and at another standing close together and 

 forming a kind of brush, but although this brush would be a new 

 character of the beetle, yet its development would depend upon 

 quantitative differences, namely, on the fact that the same skin-area, 

 which in the first ease bore perhaps only one hair, had in the second 

 case a hundred. The quantity of hair cells has notably increased 

 upon this small area. In the same way the characteristic striping of 

 the zebra depends not on a qualitative change in the skin as a whole, 

 but upon an increased deposit of black pigment in particular cells of 

 the skin, therefore on a quantitative change. In relation to the 

 whole animal it is a qualitative variation, as contrasted, for instance, 

 with the horse, but in respect of the constituent parts which give 

 rise to the qualitative variation it is purely quantitative. The 

 character of the whole edifice is changed when the proportion of 

 the stones of which it consists are altered. 



Thus the determinants of the germ may not only become larger 

 or smaller as a whole, but some kinds of the biophors of which they 

 are made up may increase more than others, under definite altered 

 conditions, and in that case the determinants themselves will vary 

 qualitatively, so that, from the changing numerical proportions of 

 the different kinds of biophors, a variation of the characters of the 

 determinants can arise, and consequently also qualitative variations 

 of the organs controlled by the determinants — the determinates. 

 But, since nothing living can be thought of as invariable, the biophors 

 themselves may, on account of nutritive fluctuations, grow unequally, 



