HEREDITY. 65 



III. Organic Continuity between Generations. — 

 Heredity. 



Every one knows that like tends to beget like, that offspring 

 resemble their parents, and sometimes their ancestors 

 (atavism). Not only are the general characteristics trans- 

 mitted, but minute features, idiosyncrasies, pathological 

 conditions, innate or congenital in the parents, may be 

 transmitted to the offspring. 



Many attempts have been made to explain this, but the 

 first suggestion with any scientific pretensions was that the 

 reproductive cells, which may become offspring, consist 

 of samples accumulated from the different parts of the body. 



This was a very old idea, but Herbert Spencer and 

 Charles Darwin gave it new life. According to Darwin's 

 " provisional hypothesis of pangenesis," the reproductive 

 cells accumulate gemmules liberated from all parts of the 

 body. In development these gemmules help to give rise to 

 parts like those from which they originated. This hypothesis 

 has been repeatedly modified, but, except in the general 

 sense that the body may influence its reproductive cells, 

 " pangenesis " is discredited by most biologists. 



The idea which is now accepted with general favour is, 

 that the reproductive cells, which give rise to the offspring, 

 are more or less directly continuous with those which gave 

 rise to the parent. This idea, suggested by Owen, Haeckel, 

 Rauber, Galton, Jager, Brooks, Nussbaum, and especially 

 emphasised by Weismann, is fundamentally important. 



At an early stage in the development of the embryo the 

 future reproductive cells of the organism are distinguishable 

 from those which are forming the body. The latter develop 

 in manifold variety, and as division of labour is established, 

 lose their likeness to the fertilised ovum of which they are 

 the descendants. The future reproductive cells, on the other 

 hand, are not implicated in the formation of the body, but 

 remaining virtually unchanged, continue the protoplasmic 

 tradition unaltered, and are thus able to start an offspring 

 which will resemble the parent, mainly because it is made of 

 the same protoplasmic material. 



A fertilised egg-cell with certain characters (a, b, c), 

 develops into an organism in which these characters are 



E 



