326 The Study of Animal Life part iv 



to the works of Galton, Ribot, Brooks, Herdman, Plarre, 

 Van Bemmelen, and De Vries. 



3. The Modern Theory of Heredity. — In the midst of 

 much debate it may seem strange to speak of the modern 

 theory of heredity, but while details are disputed, one clear 

 fact is generally acknowledged, the increasing realisation of 

 which has shed a new light on heredity. This fact is the 

 organic continuity of generations. 



In 1876 Jsger expressed his views explicitly as follows : 

 " Through a long series of generations the germinal proto- 

 plasm retains its specific properties, dividing in develop- 

 ment into a portion out of which the individual is built up, 

 and a portion which is reserved to form the reproductive 

 material of the mature offspring." This reservation, by 

 which some of the germinal protoplasm is kept apart, during 

 development and growth, from corporeal or external influ- 

 ences, and retains its specific or germinal characters intact 

 and continuous with tliose of the parent ovum, Jagger 

 regarded as the fundamental fact of heredity. 



Brooks (1876, 1877, 1883) was not less clear: "The 

 ovum gives rise to the divergent cells of the organism, but 

 also to cells like itself. The ovarian ova of the offspring 

 are these latter cells or their direct unmodified descendants. 

 The ovarian ova of the offspring thus share by direct 

 inheritance all the properties of the fertilised ova." 



But before and independently of either Jasger or Brooks 

 or any one else, Galton had reached forward to the same 

 idea. We have noticed that he was led in 1872 to the 

 conclusion that "the doctrine of pangenesis, pure and 

 simple, is incorrect." His own view was that the fertilised 

 ovum consisted of a sum of germs, gemmules, or organic 

 units of some kind, to which in entirety he applied the 

 term stirp. But he did not regard this nest of organic 

 units as composed of contributions from all parts of the 

 body. He regarded it as directly derived from a previous 

 nest, namely, from the ovum which gave rise to the pareiit. 

 He maintained that in development the bulk of the stirp 

 grew into the body^ — as every one allows — but that a cer- 

 tain residue was kept apart from the development of the 



