124 CIRCUMSTANCES FAVOURABLE TO THE [Chap. IV. 



in the case of flowers, I have as yet failed, after consulta- 

 tion 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 impos- 

 sible. 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 s;enus, though 

 aOTeeino- closelv with each other in their whole orsanisa- 

 tion, 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 indi- 

 viduals is a very general, if not universal, law of nature. 



Circumstances favourable for the production of new forms 



through 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 



