1888-89.] Mr J. A. Thomson on Theory of Heredity , 
95 
gested by Darwin in his Variation of Animals and Plaids under 
Domestication. The chief suggestions of this theory are well 
known to be as follows : — 
(1) Every cell of the body, not too highly differentiated, throws 
off characteristic gemmules ; 
(2) These multiply by fission, retaining their characteristics ; 
(3) They become specially concentrated in the reproductive 
elements ; 
(4) In development the gemmules unite with others like them- 
selves, and grow into cells like those from which they were 
originally given off. 
The applications of this, in one sense very satisfactory theory, to 
the phenomena of atavism, and reappearance of similar characters 
at similar times, do not concern us in this general survey. 
Jdgefs Theory .— The next theory is somewhat difficult to sum- 
marise, partly because of its technical character, partly because the 
author does not appear to be quite consistent in his statement of it 
at different times. The main points, under the present section, are 
as follows : — 
(1) Each organ and tissue contains, along with the molecules of 
its albumen, a specific “scent-stuff” (Duft-und-Wiirzestoff). 
(2) In hunger and similar experience the albumen liberates the 
“scent-stuff,” which penetrates through the body as fatty 
acids, ethers, &c. 
(3) These are specially attracted to the reproductive cells, which, 
when mature, are thus specialised by the reception of scent- 
stuff, and have in their protoplasm vires formativse enough 
to reproduce a new T organism like the parent. 
It will be seen later on that this hypothesis of chemical pan- 
genesis is not the most important contribution made by the author 
to the theory of heredity. 
Gallon's modified Theory of Pangenesis . — From experiments on 
the transfusion of blood, Galton was led to conclude that “the 
doctrine of pangenesis, pure and simple, is incorrect.” But he did 
more than urge serious objections against Darwin’s theory ; he for- 
mulated one of his own, to which, with the exception of Professor 
Herdman, subsequent investigators do not appear to me to have 
