II INTEGUMENTARY VARIATIONS 89 



dogs. Similarly, as Roulin notices, poultry have, in 

 Colombia, lost their feathers, and while the young are 

 at first covered with a black and delicate down, they 

 lose it as they grow in great part, and the adult fowls 

 nearly realize Plato's realistic description of man 

 a biped without feathers. Conversely, many animals, 

 when transferred from warm to cold climates, acquire 

 a thicker covering, dogs and horses, for instance, be- 

 coming covered with wool, &c. Such cases are easily 

 observed in Europe when animals from the warm 

 regions are sent to our zoological gardens. In 

 Paris, for instance, we have seen sheep from Senegal 

 acquire, in the course of two years, a long and grizzled 

 cover of hair, while at first they had but a short one. 

 Similar modifications have been observed in a large 

 number of animals, and more precise data could have 

 been obtained if more attention had been paid to the 

 subject. As M. Faivre rightly remarks in his La 

 Variabilite des Especes et ses Limites (1868), while 

 " no truth is better established in natural history 

 than the influence of climate on the superficial cha- 

 racter of animal species, on the dimensions, colour, 

 form, nature of integuments and hairs, none has been 

 less investigated and discussed by the naturalists 

 whose business is to distinguish one might even 

 say, to multiply species." 



Variability and variation of such superficial cha- 



