504 The American Naturalist. [June, 
antecedent to that of Darwinism, since it accounts for the 
primary diversification of species on the basis of inequalities 
of cell-nutrition in all forms, thus seizing upon the diversifica- 
tion of the physiological powers of the primal forms of life as 
the first factors in biological evolution, and which gave the lat- 
ter its first impulse and upon which all further impulses have 
been superimposed. 
i8. Sexuality isthus rendered the motive force of all bio- 
logical development, but in a totally different sense from that 
hitherto held by any one else. 
19. While sexuality thus viewed becomes the motive force 
of all biological evolution it also gives rise to the means of 
variability and a greatly augmented fertility of individuals, 
thus also leading to the struggle for existence and natural se- 
20. Sexuality is therefore found to transcend in importance 
the principle of natural selection itself, since over-nutrition 
only could have led to the over-production of germs and the 
consequent increase of individuals in a geometrical ratio, as 
assumed by the Darwinian hypothesis, and, since the vege- 
table world stands in an annectant relation between the not- 
living and animal world, it can be understood how the latter 
came to be over-nourished. 
21. This hypothesis further assumes that, with the gradual 
circumscription and locaHzation within more and more restricted 
limits, of the production of germ-cells, and pari passu with 
morphological differentiation, that the reproductive and reca- 
pitulative powers of the other cells of multicellular organisms 
became gradually less and less marked, owing to the gradually 
"lore intensified expression of the principle of the physiologi- 
cal division of labor in the evolution of organs with more and 
more definite functions. 
22. It regards the hypothesis of the immortality and immu- 
tability of the Keimplasma as inadequate, and as absolutely 
disproved by the facts of morphological development alone. 
23. The production of germ-cells has been localized more 
and more definitely as a result of the increasing morphological 
specialization of multicellular forms, so that the the hypothe- 
sis which assumes that the germ-plasma is precociously set 
aside in order to render it unmiscible with the somatic 
plasma, and therefore immortal, is based upon a fundamental 
error of interpretation of the facts of morphology. 
24. The only cells in the multicellular forms which are ab- 
