74 CIRCUMSTANCES FAVOURABLE TO THE [CHAP. IV. 



cross. As in the case of flowers, I have as yet failed, after con- 

 sultation with one of the highest authorities, namely, Professor 

 Huxley, to discover a single hermaphrodite animal with the 

 organs of reproduction so perfectly enclosed 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, under this point of view, a case of great 

 difficulty; but I have been enabled, by a fortunate chance, to 

 prove that two individuals, though both are self -fertilising herma- 

 phrodites, do sometimes cross. 



It must have struck most naturalists as a strange anomaly that, 

 both with animals and plants, some species of the same family 

 and even of the same genus, though agreeing closely with each 

 other in their whole organisation, are hermaphrodites, and some 

 unisexual. But if, in fact, all hermaphrodites do occasionally 

 intercross, the difference between them and unisexual species is, 

 as far as function is concerned, very small. 



From these several considerations and from the many special 

 facts which I have collected, but which I am unable here to give, 

 it appears that with animals and plants an occasional intercross 

 between distinct individuals is a very general, if not universal, 

 law of nature. 



Circumstances favourable for the production of new forms throiiyh 

 Natural Selection. 



This is an extremely intricate subject. A great amount of 

 variability, under which term individual differences are always 

 included, will evidently be favourable. A large number of 

 individuals, by giving a better chance within any given period for 

 the appearance of profitable variations, will compensate for a 

 lesser amount of variability in each individual, and is, I believe, 

 a highly important element of success. Though Nature grants 

 long periods of time for the work of natural selection, she does 

 not grant an indefinite period ; for as all organic beings are 

 striving to seize on each place in the economy of nature, if any 

 one species does not become modified and improved in a cor- 

 responding degree with its competitors, it will be exterminated. 

 Unless favourable variations be inherited by some at least of the 

 offspring, nothing can be effected by natural selection. The 

 tendency to reversion may often check or prevent the work ; but 

 as this tendency has not prevented man from forming by selection 

 numerous domestic races, why should it prevail against natural 

 selection ? 



In the case of methodical selection, a breeder selects for some 

 definite object, and if the individuals be allowed freely to inter- 

 cross, his work will completely fail. But when many men, without 



