1889. J Embryology. 503 
10. The aggregation of large masses of segmentable plasma 
has also enabled the products of such simultaneous and suc- 
cessive segmentations to cohere and remain a multicellular ag- 
gregate, and to thus lay the foundations and become the direct 
cause of all metazoan and metaphytic organization. 
11. The over-nutrition of the female element and the aug- 
mentation of its mass has rendered possible complex series of 
simultaneous and successive segmentations, in planes of from 
one to three dimensions, and the development of embryos 
without need of other nutriment during the preliminary or 
larval stages of ontogeny, thus leading also to the evolution of 
all larval forms. 
12. So long as living organisms remained unicellular they 
were enabled to vary and become adapted only within the nar- 
row limits determined by their unicellular condition, yet we 
know how marked is variability, even in this low grade of de- 
velopment ; proportionally far greater than in multicellular 
types. 
13. The achievement of the multicellular condition, as I 
have supposed, produced new and more complex morphologi- 
cal relations leading to the manifold differentiation of physio- 
logical functions in relation to diversification of surroundings, 
thus introducing a new and most powerful cause or capacity 
for variations and adaptations under such diverse conditions. 
14- It is thus seen that the evolution of sexuality is the in- 
direct cause of variability, and that otherwise there could have 
been no such thing as a struggle for existence leading to nat- 
ural selection amongst multicellular organisms— at least seeing 
that they must have been produced, according to this hypoth- 
esis, as a result of the development of sexuality. 
15- Over-nourishment in the vegetable, then lead to the 
over-nourishment of the animal world and the over-produc- 
tion of germs or young in both, so that the rate of increase 
became augmented in a geometrical ratio, as supposed upon 
the Darwinian hypothesis, which, on the basis of the theory 
of the struggle for existence and the process of natural selec- 
tion so evoked, accounts for the preservation of valuable or 
advantageous variations through survival and inheritance. 
16. Over- nourishment, then, is, according to the present 
hypothesis, regarded as the primary cause of morphological 
differentiation under the stress of diverse conditions, as well as 
of the geometrical ratio of increase of such forms, and, conse- 
quently, of the struggle for existence. 
17. The doctrine of over-nutrition consequently becomes 
