158 ACQUIRED CHARACTERS SEC. 



its dimensions and its capabilities during the individual life 

 simply in consequence of a change of habit." 



By this example the zoologist will be immediately reminded 

 of the fact that many of our domestic animals have a 

 larger intestine than the wild species from which they are 

 derived. Other morphological differences between the wolf 

 and the dog having been sought in vain, one zoologist has 

 recently attempted to make this difference in the length of 

 the intestine serve as such. But it is clear that this is only 

 a difference due to physiological conditions ; it is evidently 

 caused by the difference in the food of the domestic and the 

 wild animal. The wolf feeds upon flesh, the dog has to 

 accustom himself to vegetable food also. The domestic cat, 

 also evidently from the same causes, has a longer intestine 

 than the wild cat. It is a universal fact that, among wild 

 animals, the carnivorous have a much shorter intestine than 

 the herbivorous. In the development of the frog the two 

 types succeed one another, clearly in relation to the food. 

 The tadpole, which feeds principally on Algse, to some extent 

 on Infusoria, has an intestine of surprising length ; the adult 

 frog, feeding only on small animals, has a very short intestine. 

 It is very natural that a shorter gut suffices for the nutritious 

 food of the flesh-feeders, while the less nutritious vegetable 

 food, in order that the necessary nutriment may be got from 

 it, must be taken in larger quantities and digested for a 

 longer time. Therefore a longer intestine is useful to the 

 vegetable-feeder. 



But in what way has the gut been lengthened in the 

 domestic animals which live partially on vegetable food ? 



That this has been brought about by selection cannot 

 certainly be supposed, for although the longer intestine is an 

 advantage to the nutrition of the dog and cat, yet the differ- 

 ence in this respect between the tame and the wild animal is 

 not so great that the life of the animals in a domesticated 



