CHAPTER IV 



SHIFTS FOR A LIVING 



1. Insulation 2. Change of habit and habitat 3. Parasitism 

 4. General resemblance to surroundings 5. Variable colour- 

 ing 6. Rapid change of colour 7. Special protective resem- 

 blance 8. Warning colours 9. Mimicry --10. Masking 11. 

 Combination of advantageous qualities 12. Surrender of parts 



THE struggle for existence includes all the reactions and 

 responses which living creatures, by their very nature 

 insurgent, make to the difficulties and limitations that 

 encompass them. Some of the answers are very effective 

 and become .established as adaptations of habit and 

 habitat, structure and device. We may speak of them, 

 somewhat loosely we confess, as shifts for a living. 



1. Insulation. Some animals have attained to tem- 

 porary security through no merit of their own, but as 

 the result of geological changes which have insulated 

 them from their enemies. Thus, in Cretaceous times 

 probably, the marsupials which inhabited the Austra- 

 lasian region were insulated. In that region they and 

 the egg-laying Monotremes were for long the only re- 

 presentatives of Mammalia, and so, excepting the " native 

 dog," some rodents and bats, and more modern imports, 

 they still continue to be. By their insulation they were 

 saved from that contest with stronger mammals in which 

 all the marsupials left on the other continents were 

 exterminated, with the exception of the American 

 opossums and Selvas, whose shy, quiet ways have saved 

 them. A similar geological insulation accounts for the 

 large number of lemurs in Madagascar. 



2. Change of Habit and Habitat. It seems justifiable 



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