268 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 
In this chapter the writer has purposely avoided entering into the 
more elaborate intricacies of the Weismannian theories of develop- 
ment and heredity. The theories have been so generally discredited 
and play so small a part in modern biological thought that it seems 
useless to burden the reader’s mind with needless complexities. 
Certain other phases of ‘Weismann’s work, especially his ideas of 
the germ plasm, its separateness and its continuity, are more appro- 
priately studied in connection with genetics than at the present time. 
ROUX’S THEORY OF INTRASELECTION OR THE BATTLE OF THE PARTS 
In point of time this theory antedates Weismann’s theories, since 
it was proposed in 1881. In some respects it is a more acceptable 
theory than germinal selection, but in others quite unacceptable. 
The theory is designed primarily to explain the origin of the ‘“‘fine and 
delicate inner adaptations” of organisms, which do not come in con- 
tact with the external environment and therefore could not be directly 
affected by it. The idea is that there is a sort of struggle among the 
tissues for a chance to develop in the direction of functional perfection. 
Certain contacts, stresses, and pressures of part on part aid or hinder 
the development of parts. Thus, where muscular pressure on bone 
is greatest or weight borne by bone is greatest there will the most bony 
tissue be laid down in the form of lamellae. The result is that any 
given bone improves its structure by resistance to strain and pressure, 
which is a case of improvement with use. We may then inquire how 
such a change in the individual could affect the evolution of the race. 
The only reply involves the adoption of a distinctly Lamarckian con- 
cept, and this at present is quite unacceptable. 
COINCIDENT SELECTION OR ORGANIC SELECTION 
This theory has been masked under various guises. In addition 
to the two titles given above, it has appeared under the names “onto- 
genetic selection” and “orthoplasy.” The main idea, according to 
Herbert, is that ‘‘the individually acquired characters, though not 
transmitted to the offspring, serve to tide the successive generations 
over the critical period until germinal (inborn) variations of the 
same kind appear which are inheritable. Ontogenetic (individually 
acquired) adaptations and natural selection work together towards the 
same end. 
“This hypothesis would help to account for two related difficult 
points in the theory of natural selection. Firstly, it would explain 
the possibility of the slow accumulation of germinal variations in their 
