72 THE DARWINIAN THEORY 



distributed in the plains of Patagonia and Tierra del 

 Fuego. 



Camels are thus distributed over two areas, com- 

 prising the mass of two continents, divided by a 

 great ocean ; one area being north of the equator, 

 the other south of it, and separated by half the 

 circumference of the globe. They are animals of 

 large size, and it is hardly possible for their existence 

 to have been overlooked. Hence we may assume 

 that their geographical distribution is known 

 correctly. 



This is a good example of the difficulties in 

 accounting for geographical distribution, and of 

 the way in which they may be met. Evolution 

 tells us that close anatomical resemblances mean 

 near kinship, and forbids us to contemplate the 

 possibility of animals, agreeing in a number of 

 important points, having come into existence in- 

 dependently. 



The anatomical characters of camels are well 

 marked; they have two toes — viz., the third and 

 fourth, and walk on the palmar surface of the middle 

 phalanx, not on hoofs. The sole of the foot is 

 formed by broad integumentary cushions, and the 

 nails are small and flattened. The stomach 

 consists of a paunch with smooth lining, pro- 

 vided with two groups of water-cells with narrow 

 mouths. The cervical vertebrae are peculiar, in 

 that the canal for the vertebral artery pierces 

 the arch of the vertebra, instead of the transverse 

 process. 



The theory of gradual modification of animals 



