1897] RELATION OF MODIFICATIONS TO HEREDITY 249 
He supposes first that under appropriate circumstances a small 
amount of the original substance may be capable of governing the 
course of the future organism, just as the mathematician may con- 
struct from a small portion of a curve its whole extent. And, 
secondly, — 
“Tf in a parental organism, by long habit or constant practice, 
something grows to be second nature, so as to permeate, be it ever 
so feebly, its germinal cells, and if the germinal cells commence an 
independent life, they will aggrandise and grow till they form a 
new being, but their single parts still remain the substance of the 
parental being.” 
The objections to this theory le, I think, in the fact that direct 
communication with the reproductive organs becomes with increas- 
ing specialisation increasingly difficult, and therefore heredity and 
reproduction would cease when a certain point in the specialisation 
was reached. 
Nevertheless, some kind of provisional theory such as the fol- 
lowing would, I believe, explain better than any other theory most 
of the phenomena of inheritance :— 
(1) That in every cell there are certain reproductive units 
which are necessary to the development of that par- 
ticular cell. 
(2) That these reproductive units having a very complicated 
structure (being composed of specialised protoplasm), are 
capable of modification when acted on by external forces. 
(3) That the various impressions made upon the cell would of 
necessity be made upon these units also, and that this 
impression will be proportional to the length of time and 
intensity of the impression made. 
(4) That as specialisation of tissue occurs, each reproductive 
unit will tend to reproduce its own history, past im- 
‘pressions becoming with each successive addition more 
and more blurred. 
(5) That the stronger and more numerous the past impressions, 
the more difficult will it become for present impressions 
to affect them, hence progressively diminished power of 
use-inheritance. 
(6) That the reproductive units have the power of self multi- 
plication when in the latent condition, and that this 
multiplication will be difficult in proportion to their 
specialisation and complexity. Hence latent germs 
would tend to be carried on from one generation to 
another, and increase the general stability of the 
organism. 
