CHAPTER IV 



ANIMALS AND THE PHYSICAL ENVIRON- 

 MENT : GENERAL RELATIONSHIPS 



General Relationships 



We have considered the surroundings in which 

 the desert animals live, and seen that the chmate 

 and other physical factors are generally unfavourable 

 to ordinary animal life. We shall now study some 

 of the adaptations which enable the animals to 

 overcome the obstacles of their physicietl environment, 

 and to draw sustenance from the specialized flora of 

 the desert. 



Every element of the desert climate is liable to 

 rapid fluctuations, which are often quite irregular : 

 and in many desert places the great heat and 

 drought, and violent winds and other climatic factors, 

 all combine during the summer to be most hostile 

 to the flora and faima. 



The habit of aestivation in plants has been already 

 referred to (pages 57-59). A similar habit is common 

 in the invertebrate animals of desert faunas. In 

 the present state of knowledge we can only attribute 

 it in broad terms to the extreme hostility of the 

 summer climate ; but it may well be that as we 

 study the effects of varying temperature, or humidity, 



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