1888-89.] Mr J. A. Thomson on Theory of Heredity. 101 
(1) “In each development a portion of the specific germinal 
plasma (‘ keimplasma ’), which the parental ovum contains, 
is not used up in the formation of the offspring, but is 
reserved unchanged for the formation of the germinal cells 
of the following generation.” 
(2) What is actually continuous is the germinal protoplasm — the 
“ keimplasma ” — “ of definite chemical and special molecular 
constitution.” A continuity of germinal cells is now rare ; 
a continuity of intact germinal plasma is constant. 
(3) This keimplasma has its seat in the nucleus, is extremely 
complex in structure, but has nevertheless an extreme power 
of persistence (von ungemein grossem Beharrungsvermogen), 
and enormous powers of growth. 
Y. Elaborations of Doctrine of Continuity. 
It may now be concluded that in the more or less strict continuity 
of the successive sets of reproductive elements lies the solution of 
the main problem of heredity. This appears the most convenient 
place to notice the various suggestions made as to what it is exactly 
that is continuous. The earlier of these suggestions were brought 
forward indeed before the notion of continuity had its present 
definite form, but I have deemed it better to^introduce them here 
than to mix them up with the pangenetic series. 
In the simplest animals, organism A buds and hands on a fraction 
of its living matter to A', surely A' being so really continuous with 
A, must grow into a form like its origin. But while emphasising 
that the explanation of the similarity lies in the continuity, we may 
probe further into the continuity itself, and express it in chemical, 
physical, or even psychical terms. 
So with higher organisms. A germ x develops into a body, and 
the reproductive cells thereof. The latter arise in such a way that 
they are virtually continuous with the undifferentiated original 
germ x. They retain its constitution intact, become the starting 
points of new organisms, which from similar origins are naturally 
similar in result. The whole emphasis is laid on the notion of con- 
tinuity, but it is necessary to consider the attempted analyses made 
at different levels. 
The Memory Theories. — Hering in Prag and Samuel Butler in 
