1889.] Embryology. 505 
solutely otherwise functionless are the germ-cells. They alone, 
therefore, can become the vehicles for the transmission of all the 
traits of the parent in higher forms, since they alone are other- 
wise functionally unoccupied, and are the only cells of the 
body which, by any stretch of the imagination, can be sup- 
posed, a priori, to possess the recapitulative power manifested 
in ontogeny, 
25. It further assumes that the theory of the geometrical 
ratio of increase is qualified by the advent of multicellular 
forms as a direct result of the development of sexuality, and 
that, reckoning on the basis of cell generations, the ratio of 
increase in the animal and plant world is absolutely and rela- 
tively less than if living forms had remained unicellular. 
26. It leads also to the assumption that biological evolution 
has been along definite lines, and not fortuitous or hap-haz- 
ard, as has been tacitly or avowedly assumed by some incau- 
tious but extreme partisans of the doctrine of natural selec- 
27. This hypothesis is based on the assumption that the 
undifferentiated nucleated cell is the point of departure for 
all morphological and physiological differentiation, and that 
the first depends upon the character of the karyokinetic changes 
which go on within it, while the second depends upon the na- 
ture of its metabolism and the mechanical arrangement and 
constitution of the plasma through which such metabolism is 
manifested. 
28. Upon this ground may be based a further development 
of hypothesis which gives a satisfactory explanation of par- 
thenogenesis, paedogenesis, gemmation, temnogeny, metagene- 
sis, and the recapitulative processes of ordinary sexual 
genesis. 
29. In the production of female germs (ova, oospheres,) 
there occurs a prolonged process of intergration of plasma to 
increase the volume of the cell-body. In the production of 
male elements, (spermatozoa, antherozoids,) on the contrary, 
an actual process of elimination of plasma occurs, so as to re- 
duce the cell-body to a minimum size and leave little remain- 
ing except the nucleus and its chromatin. The modes of 
production of the male and female elements therefore, stand in 
the most extreme contrast in respect to each other. 
This hypothesis, founded upon data which have been hither- 
to apparently ignored, applies to both the animal and vege- 
table kingdoms, sex having probably arisen simultaneously 
