282 The New Factor in Organic Development . [May, 
that the principle of the struggle for existence, which 
is of course merely Natural Selection viewed from a 
slighty different stand-point, was first propounded by 
Heraclitus, with whom conflict, strife was the author of all 
things. 
It must be admitted that Lamarck’s principle, the action 
of use and disuse, furnishes a more diredt explanation of the 
purposive than does Natural Seledtion. This principle has 
scarcely been sufficiently appreciated and followed out. 
Experimental evidence is wanting as to how far the modifi- 
cations produced by use or disuse are hereditary. It seems 
to us, also, that many authors who admit that a muscle, an 
eye, &c., can be strengthened and improved by use, or, on 
the other hand, more or less completely atrophied by disuse, 
have overlooked the truth to which Prof. Du Bois-Reymond 
draws attention in a memorable discourse lately reviewed in 
the Journal of Science (1882, p. 165). The increase in bulk 
of a muscle as occasioned by regular exercise, and, conversely, 
its diminution if allowed to remain inactive, cannot fail to 
modify the nervous centres. We are thus brought to the 
principle which Dr. Roux discusses at length in the work 
before us. There is not merely a struggle for existence — a 
conflict between species and species, or between individuals 
of the same species. There is also a struggle within the 
organism itself, a conflict between molecules, between cells, 
between tissues, and between organs. By this conflict, 
intimately connected as it is with the Lamarckian principle 
of use and disuse, much of the adaptation, the purposive- 
ness observed in the animal system becomes intelligible. 
Before considering more closely this internal conflict, which 
may, perhaps, be likened to the “ competition” which in a 
community takes place between individuals, classes, in- 
terests, &c., we may return for a moment to the Lamarckian 
principle. This principle has been more fully recognised by 
Haeckel than by Darwin, The former considers that if e.g. 
the wings of domestic poultry have not been reduced to a 
mere rudimentary state, the cause must be sought in the 
insufficient number of generations which have elapsed since 
these birds were brought under human influence and in the 
circumstance that with them the struggle for existence is 
not very intense, so that the principle of “ organic economy” 
does not come into play. Darwin, in his work on the 
“ Variation of Animals and Plants under Domestication,” 
lays a greater weight on the effects of use and disuse than 
he does in the “ Origin of Species.” Dr. Roux, after noting 
the somewhat perfunctory manner in which this question 
