RELATIONS AND SURROUNDINGS. I2Q 



together. Some have only pigment spots that give an 

 impression of light, perhaps; others have such a perfection 

 of eye structure that they see light and in addition distin- 

 guish colors, have from it a sense of direction, and get 

 an image of external objects. 



All animals are adapted to temperature in some degree ; 

 but some become so by an external covering of feathers, 

 as the birds; others, as the whales, have a layer of fat 

 beneath the skin which serves the same purpose. Many, 

 by rapid oxidation, produce enough body heat to control 

 their internal temperature ; others do not, and are spoken 

 of as cold-blooded. 



142. Practical Exercise. In a similar way, trace out some of the 

 variations in the special manner and degree of adaptation to the 

 various items under "A," found in animals of your acquaintance. 



1 43 . Adaptations Among Animals of the Same Species. 



These relations are an interesting mixture of competi- 

 tion and co-'operation. In many species the parents 

 instinctively make great personal sacrifice that the off- 

 spring may be cared for; the offspring, on the other hand, 

 contend with one another for this parental provision. In 

 some instances the young actually devour one another. 

 Each individual thus possesses both friendly and com- 

 petitive habits and relations with the members of his 

 own species. 



144. Mating Adaptations. One of the most striking 

 series of adjustments found in animals are those which 

 adapt the two sexes to each other. Indeed, the two cells 

 which unite, and which represent the sex qualities, are 

 themselves adapted in an interesting fashion. The male 

 cell is poorly nourished and active ; the female cell is w r ell 

 nourished and sluggish. They supplement each other, 



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