THE RAW MATERIALS OF EVOLUTION 111 



" If, as I must think, external characters produce 

 little direct effect, what the devil determines each 

 particular variation ? " 



Having made this confession of ignorance, we 

 venture to discuss the possibilities of answer to a 

 question which can never be far from any thought- 

 ful mind. 



There are variations and variations. There are 

 variations that mean nothing more than an aug- 

 mentation or diminution of an already existing 

 quality. The hair may be very long or the tail 

 very short. Or a variation may mean that a 

 character present in parents and ancestry is absent 

 from the offspring : the entail has been broken. 

 An albino expresses such a variation, or a hornless 

 calf, or a tailless kitten. Or, again, a variation 

 may be interpretable as a novel arrangement of 

 characters or qualities which were present in the 

 ancestry. A piebald pony may serve as a diagram. 



Now, in regard to variations of this sort 

 which may be described as permutations and 

 combinations of the already existing unit char- 

 acters the modern knowledge of the conditions 

 of heredity has made it plain that there are many 

 opportunities for their occurrence before, during, 

 and after fertilisation. We know that each germ- 

 cell contains a definite number of stainable bodies, 

 or chromosomes, which appear to be the bearers 

 of the heritable qualities. We may compare these 

 to a microscopic pack of cards, and we may say 

 th there is an extraordinarily elaborate shuffling 

 beiore development begins. Half of the pack is 

 ejected from the egg-cell in what is known as a 

 " polar body," and the number is raised to the 

 normal again (constant throughout the body of the 



