
go The American Naturalist. [January, 
of the germ-cells would be thus impressed by changes in the manner 
of exhibition of the metabolism of the bodies of the parent fishes 
there can scarcely be any question. 
In fact, if it is borne in mind that the extremely unspecialized and 
functionless condition of the germinal plasma is in itself favorable to 
variation through its impressibility by imperceptible changes in external 
conditions, we should almost cease to wonder at the variability of 
multicellular animals, which, as is well known, is always intensified 
under the influence of domestication. 
It may not be generally known that abundant food and inappreciable 
variations of the conditions of life exert a most astonishing influence 
upon the size, form, rate of multiplication, and tendency toward con- 
jugation in ciliated infusoria, The individuals differ in size by many 
times the bulk of the smallest condition of the same species, and there 
are equally great and unaccountable differences in form arising from 
unknown causes, as I learn by keeping the same colonies under pro- 
longed observation, and no less than two very distinct and highly 
characteristic modes of fission may occur in the same species, whether 
free or attached in habit. So great are these differences that I am 
convinced that individuals of one and the same species have been 
regarded in some instances as distinct species by different observers 
who have not observed the same form under a great variety of con- 
ditions. . 
In an earlier essay,‘ giving synoptically the results of an extended 
study of the subject of sex, I assumed that the egg, or odsperm, was in- 
herently more capable of variation in its early stages of development 
than during the later larval or adolescent period. This is what should 
have been expected if my hypothesis of the nature of heredity and 
the causes of variation is true, no less than upon the ground of the 
known want of morphological specialization characterizing all the 
germs of multicellular organisms. If we seek for facts in support of 
this view, we have them in abundance in the extreme sensitiveness of 
the ova of many metazoa to outward influences of the most trivial 
character. I may cite in illustration the well-known experiments of l 
Weber in producing monstrosities from the recently fertilized eggs of 
the soc by simply shaking them somewhat roughly. To the same 
t speaks the fact, well-known to fish-culturists, that the eggs of 
Salmonidæ immediately after fertilization must be handled with ex- 
treme care, some experienced persons declaring that it is even dan- 
gerous to disturb them in any way for the first few days, lest the 
* Origin and Meaning of Sex. AMER. NATURALIST, pp. 501-508, Vol. XXIII., 1889 




