XVIII. THE CRAYFISH. A STUDY OF ADAPTATIONS 



Problem XXIX. A study of tlu> idea of adaptations as shoivn 

 ill the crayfish {optional). (Laboratory Manual, Proh. XXI A!.) 

 (a) Protection, 

 ib) Locomotion, 

 (c) Surroundings, 

 id) Feeding, 

 (e) Breathing. 



Adaptations. — Plants and animals are in a continual struggle 

 to hold the places they have obtained upon the earth. Continually 

 we see garden plants driven out or killed by the competing weeds, 

 simply because the weeds are better fitted or adapted to live under 

 the conditions which exist in the garden, especially if it is unculti- 

 vated. An adaptation in a plant or animal is some structure, habit, 

 or ability which is of advantage to the organism in its battle for 

 life. We have seen many examples of adaptations in plants, — 

 adaptations in flowers for securing cross-pollination, in fruits for 

 seed-scattering, in young plants for protection, in roots for water- 

 securing ; the list is endless. 



In animals, likewise, the successful competitors are the ones with 

 adaptations to fit them for living in the particular environment or 

 surroundings in which nature has put them. Examples are often 

 seen where animals, like sheep or goats, which have a woolly cover- 

 ing, when introduced by man into a warmer country, die because 

 the outer coat is too warm. An adaptation for withstanding cold 

 becomes harmful to the animal under conditions of greater heat. 



One adaptation which we have already noticed in animals is 

 always protective. This is resemblance of the animal to the sur- 

 roundings in which it lives. Other adaptations aid the animal in 

 obtaining and digesting food, in protecting itself or its young 

 from attack by enemies, and in many other ways aiding the animal 

 to battle successfully with the dangers around it. 



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