Chap. IV. 
OF INTERCKOSSING. 
101 
cuiTents in the water offer an obvious means for an occa¬ 
sional cross. And, as in the case of flowers, I have as yet 
failed, after consultation with one of the highest autho¬ 
rities, namely. Professor Huxley, to discover a single case 
of an hermaphrodite animal with the organs of reproduc¬ 
tion so perfectly enclosed within the body, that access 
from without and the occasional influence of a distinct 
individual can be shown to be physically impossible. 
Cirripedes long appeared to me to present a case of 
very great difficulty under this point of view; but I 
have been enabled, by a fortunate chance, elsewhere to 
prove that two individuals, though both are self-fer¬ 
tilising hermaphrodites, do sometimes cross. 
It must have struck most naturalists as a strange 
anomaly that, in the case of both animals and plants, 
species of the same family and even of the same genus, 
though agreeing closely with each other in almost their 
whole organisation, yet are not rarely, some of them 
hermaphrodites, and some of them unisexual. But if, in 
fact, all hermaphrodites do occasionally intercross with 
other individuals, the difference between hermaphrodites 
and unisexual species, as far as function is concerned, 
becomes verv small. 
•/ 
From these several considerations and from the many 
special facts which I have collected, but which I am 
not here able to give, I am strongly inclined to suspect 
that, both in the vegetable and animal kingdoms, an 
occasional intercross with a distinct individual is a law 
of nature. I am well aware that there are, on this view, 
many cases of difficulty, some of which I am trying to 
investigate. Finally then, we may conclude that in 
many organic beings, a cross between two individuals is 
an obvious necessity for each birth; in many others it 
occurs perhaps only at long intervals; but in none, as I 
suspect, can self-fertilisation go on for perpetuity. 
