38 CIRCUMSTANCES FAVORABLE TO THE 



action of insects and of the wind with plants, by which an 

 occasional cross could be effected with terrestrial animals 

 without the concurrence of two individuals. Of aquatic 

 animals, there are many self-fertilizing hermaphrodites ; but 

 here the currents of water offer an obvious means for an occa- 

 sional cross. As in the case of flowers, I have as yet failed, 

 after consultation with one of the highest authorities, viz., 

 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 dis- 

 tinct 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 of self-fertilizing hermaphrodites, 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 organization, are hermaphro- 

 dites, 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 FAVORABLE 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 favorable. A large num- 

 ber of individuals, by giving a better chance within any given 

 period for the appearance of profitable variations, will com- 

 pensate for a lesser amount of variability in each individual, 

 and is, I believe, a nighty 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 

 fftodified and improved in a corresponding degree with its 



