OLD TYPES AND NEW 207 



brothers and sisters from the same litter at the end of 

 which time the animals were larger and more vigorous 

 than those not inbred. 



Shull found in growing Indian corn that loss of 

 vigor results from continual self-fertilization, and 

 many breeders have had similar experiences with ani- 

 mals as well as, other plants. 



In the case of the pomace fly, Drosophila, Castle 

 inbred brother and sister for fifty-nine generations 

 without diminishing the fertility of the line. 



Hornaday cites the case of the deer in the royal 

 herd at Windsor which arose from one male and two 

 females introduced from New Zealand in 1862. The 

 herd now numbers 20,000 and shows no signs of de- 

 terioration. 



No arbitrary law with respect to the effects of in- 

 breeding upon vigor and fertility can be laid down, 

 therefore, which will apply equally to all cases. 



Nature has secured, often by elaborate devices, a 

 separation of the sexes, especially among the higher 

 organisms, and in consequence there has arisen an 

 unavoidable necessity of outcrossing. The intricate 

 adaptations existing between insects and flowers, for 

 example, seem to be directed entirely toward insuring 

 outcrossing among plants. 



There are, on the other hand, various well known 

 provisions in nature to insure inbreeding. The ma- 

 jority of plants are probably self-fertilized while her- 

 maphroditic animals, which sometimes at least are self- 

 fertilized particularly among the lower forms, are very 

 common. 



