64 THE CONTROL OF LIFE 



Digression on the Origin of Novelties 

 The conditions of the appearance of these novelties 

 are not known, but the problem is the subject of interest- 

 ing speculations. There is no great difficulty in under- 

 standing how quantitative variations may arise — a 

 little more of this and a little less of that — for the germ- 

 cells go through a complicated process of maturation 

 in which the number of nuclear-bodies or chromosomes 

 is reduced to half the normal number, so that when the 

 sperm-cell and the egg-cell unite in fertilisation the 

 normal number is restored. Now, if these nuclear- 

 bodies or chromosomes be vehicles (or the vehicles) 

 of the factors of the hereditary characters (or some of 

 them), the numerical reduction in the course of the 

 ripening of the germ-cells may be a condition of variation. 

 If we compare the nuclear-bodies or chromosomes to a 

 pack of cards, there is in maturation a shufEing of the 

 cards and a division of the pack into two half-packs. 

 In the case of the ovum one half-pack is always lost 

 altogether. In fertilisation two half-packs are brought 

 together to make a new whole-pack. The metaphor 

 of the shuffling of the cards may serve without further 

 detail to suggest how quantitative variations might 

 readily arise by the dropping out of factors in the process 

 of maturation. So one might try to account for a 

 hornless calf in a horned race, or for an albino child. 

 It is well known that novelties sometimes follow the 

 crossing of two dissimilar forms, and this serves as a 

 basis for the theory that the permutations and com- 

 binations involved in the fertilisation of the egg-cell by 



