

'176 



SUMMARY OF THE 



Chap. XIX. 



crossing, asks, "an id aliquid in recessn habeat, qnod hujus- 

 cemodi flores nunquam proprio suo pulvere, sed semper eo 

 aliarum suae speciei impregnentur, merito quseritur? Certe 



natura nil facit frustra." 



Although we 



may demur to Kol- 



renter's saying that nature does nothing in vain, seeing ] 10 w 



many . organic beings retain rudimentary and useless organs 

 yet undoubtedly the argument from the innumerable contriv- 

 ances, which favour the crossing of distinct individuals of the 

 same species, 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 sepa- 

 rated localities, which can only occasionally come into contact 

 and pair, the greater vigour and fertility of the crossed offspring 

 will ultimately prevail in giving uniformity of character to the 

 individuals of the same species. 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 throw light on the cause of 

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

 interbreeding, w r e have seen that, on the one 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 effectu- 

 ally stimulated by the male element, when taken from a dis- 

 tinct 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 repro- 

 ductive 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 

 conceive. 



rarely couple : some couple freely, but never or rarely 

 The secondary male characters, the maternal func- 



tions and instincts, are occasionally affected. 



With plants 



when first subjected to cultivation, analogous facts have been 

 observed. We probably owe our double flowers, rich seedless 



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