166 



THE THEORY OF EVOLUTION 



maintained continuously in India : they become smaller, 

 slenderer and with more pointed features ; an exception 

 is the spaniel, which can be kept thoroughbred for a 

 long time by breeding. ' The Hares/ says Ch. Deperet, 1 

 ' in the level regions of North and Central France always 

 differ from those of Provence in the South by being of 

 larger dimensions, having longer and thicker hair, 

 long and thickly haired ears, and a darker fur. These 

 differences become more emphasized as we proceed 

 from Provence towards Africa. The Algerian Hares 

 are scarcely more than half as large as European ones, 

 while when the Sahara region is reached the Hares are 

 very small and of an " Isabelline " colour. . . . Similar 

 specific differences occur in the Foxes and Weasels of 

 the North and South of Europe/ 



The composition of the soil is of great importance 

 for the development of plants and more or less for 

 all plants in the same direction, hence we speak of the 

 desert, salt, and limestone flora. The shells of snails 

 are certainly influenced by the composition of the soil : 

 on soils rich in lime they are thick and wrinkled, on 

 silicious ones thin and smooth. 



Ordinary garden cress, frequently watered with 

 salt water, acquires fleshy leaves, like many plants 

 which grow on the seashore. 



Instructive are the experiments which have been 

 made with regard to the influence of temperature. 

 Our Woodnettle Moth (Vanessa levana), for instance, 

 has two forms, spring and summer. If the chrysalis 



1 Umbildung der Tierwelt, p. 116. 



