3^ THE INDUCTIONS OF BIOLOGY. 



an occasional, or a frequent, or a constant crossing between 

 flowers ; and after quoting Prof. Huxley to the effect that 

 among hermaphrodite animals, there is no case in which " the 

 occasional influence of a distinct individual can be shown to 

 be physically impossible ; " Mr. Darwin writes — " 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 in- 

 dividual is a law of nature in none, as I suspect, 



can self-fertilization go on for perpetuity." This conclusion, 

 based wholly on observed facts, is just the conclusion to which 

 the foregoing argument points. That necessary action and 

 the re-action between the parts of an organism and the 

 organism as a whole — ^that power of an aggregate to re-mould 

 the units, which is the correlative of the power of the units to 

 build up into such an aggregate ; implies that any differences 

 existing among the units inherited by an organism, must 

 gradually diminish. Being subject in common to the total 

 forces of the organism, they will in common be modified to- 

 wards congruity with these forces, and therefore towards like- 

 ness with one another. If, then, in a self- fertilizing organism 

 and its self-fertilizing descendants, such contrasts as origi- 

 nally existed among the physiological units are progressively 

 obliterated — if, consequently, there can no longer be a segre- 

 gation of different physiological units in different sperm- 

 cells and germ-cells; self-fertilization will become impos- 

 sible. Step by step the fertility will diminish, and the series 

 will finally die out. 



And now observe, in confirmation of this view, that self- 

 fertilization is limited to organisms in which an approximate 

 equilibrium among the organic forces is not long maintained. 

 While growth is actively going on, and the plwsiological units 

 are subject to a continually-changing distribution of forces, 

 no decided assimilation of the units can be expected: like 

 forces acting on the unlike units will tend to segregate them. 



