160 SUMMARY OF THE Chap. XIX. 



observer Kolreuter, after showing how well the Malvaceae 



are adapted for crossing, asks, " an id aliquid in recessu 

 habeat, quod hujuscemodi flores nunquam proprio suo pul- 

 vere, sed semper eo aliarum sua? speciei impregnentur, merito 

 quajritur ? Certe natura nil facit frustra." Although we 

 may demur to Kolreuter's saying that nature does nothing 

 in vain, seeing how many rudimentary and useless organs 

 there are, yet undoubtedly the argument from the innumer- 

 able contrivances, which favour crossing, is of the greatest 

 weight. The most important result of this law is that it 

 leads to uniformity of character in the individuals of the 

 same species. In the case of certain hermaphrodites, which 

 probably intercross only at long intervals of time, and with 

 unisexual animals inhabiting somewhat separated localities, 

 which can only occasionally come into contact and pair, the 

 greater vigour and fertility of the crossed offspring will 

 ultimately tend to give uniformity of character. But when 

 we go beyond the limits of the same species, free intercrossing 

 is barred by the law of sterility. 



In searching for facts which might throAV light on the 

 cause of the good effects from crossing, and of the evil effects 

 from close interbreeding, we have seen that, on the cne hand, 

 it is a widely prevalent and ancient belief, that animals and 

 plants profit from slight changes in their condition of life; 

 and it would appear that the germ, in a somewhat analogous 

 manner, is more effectually stimulated by the male element, 

 when taken from a distinct individual, and therefore slightly 

 modified in nature, than when taken from a male having the 

 same identical constitution. On the other hand, numerous 

 facts have been given, showing that when animals are first 

 subjected to captivity, even in their native land, and although 

 allowed much liberty, their reproductive functions are often 

 greatly impaired or quite annulled. Some groups of animals 

 are more affected than others, but with apparently capricious 

 exceptions in every group. Some animals never or rarely 

 couple under confinement ; some couple freely, but never or 

 rarely conceive. The secondary male charaetei's, the maternal 

 functions and instincts, are occasionally affected. With 

 plants, when first subjected to cultivation, analogous facts 



