CHAPTER XX 



SEASONAL CHANGES 



" A LIVING animal is almost always either acting upon its 

 surroundings or being acted upon by them, and life is the 

 relation between two variables a changeful organism 

 and a changeful environment." We ought, therefore, to 

 consider animals in relation to their surroundings. A 

 very slight acquaintance with nature will show us that 

 there are certain changes which may be ascribed to the 

 cycle of the seasons. The shedding of their antlers by 

 deer, the courting plumage of birds, the winter coats of 

 the ermine and mountain hare, the hibernation of the 

 dormouse are one and all due to outside influence. The 

 seasons bring with them, in the main, changes of tempera- 

 ture, heat and cold alternate, and these variations in 

 temperature have their direct effect on animal life. In- 

 directly animals feel the changes of the seasons ; at 

 certain periods food is scarce, at others plentiful. Other 

 externals besides the effects of the seasons play their 

 parts in moulding the lives of the creatures of the earth. 



Changes of temperature have very marked effects upon 

 most living beings. Some of these effects are obvious, as, 

 for instance, the assumption of white plumage by the 

 ptarmigan, and the paling of the fur of the variable hare 

 or of the stoat. Sometimes these effects are not so obvious 

 and can only be determined by experiment similar to that 

 of Maupas, who experimented with a single-celled animal, 

 one of the lowest in the animal kingdom. 



Let us hasten to explain that these lowly creatures 

 increase by dividing themselves into two parts, each half 

 forming a new individual. Now Maupas found that the 

 particular organism in which he was interested divided 



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