8 HEREDITARY CHARACTERS 



cells (i.e. the ovum and sperm) contain innumerable very 

 minute entities which he called " gemmules." Each of 

 these gemmules is supposed to represent a portion of matter 

 which develops eventually into a cell. Some of these 

 gemmules arise from the cells forming the body of the 

 parent, and their nature depends upon the various effects 

 of the environment upon the parent. Thus anything that 

 produces a considerable change in any part of the body of 

 the parent, will cause the cells of that part to produce a 

 particular kind of gemmule which has the potentiality of 

 producing cells like those in the parent after they have been 

 modified by the environment. Such gemmules are sup- 

 posed to travel from the various parts of the body to the 

 germ cells. According to this theory, fresh gemmules are 

 produced in every generation, their character being de- 

 pendent upon the modifications that have been produced 

 in the body of the parent by the environment. It is quite 

 evident that only a few characters can be represented by 

 gemmules produced in this way. There must be a great 

 many that owe their origin to other gemmules that existed 

 in more or less remote ancestors. We are faced by the 

 difficulty that some of the gemmules which are destined to 

 give rise to germ cells in the body of the new individual, 

 must be again divided into a sufficient number of entities 

 smaller than gemmules, which will give rise to other 

 gemmules in their turn. 1 



The theory of germinal localisation, first formulated by 

 Wilhelm His, assumes that the egg contains definite areas, 

 or definite substances, destined to produce the various parts 

 of the body. 2 According to this theory, when worked out in 

 its logical conclusion, development consists simply in the 

 dividing up of pre-existing entities or areas that represent 

 the various parts of the body. Much the same criticism as 



1 This represents only part of the theory of paiigenesis. The remainder is 

 dealt with on p. 58. 



2 His, W., Unsere Korperform und das physiologische Problem ihrer Ent- 

 stehung, Leipzig, 1874. 



