DIFFERENTIATION OF INDIVIDUALS AND ADAPTATION 



115 



useful adaptations have become useless and even hurtful from changed conditions 

 of life. 



Fig. 52. 



Fig. 52. Young Opossum {Didelphys virginiana) photographed from life by J. W. Folsom. 



Questions on the figure. — Of what conceivable value to the animal is the 

 prehensile tail? In what other groups of animals is the tail prehensile? What are 

 the habits of the opossum? How is this species distributed on the earth? Where 

 are other marsupials found? 



148. The relations of animals of the same species to one 

 another is an interesting mixture of competition and coopera- 

 tion. In the higher forms the parents instinctively make great 

 personal sacrifices that the offspring may be cared for; the off- 

 spring on the other hand struggle with each other for this 

 parental provision. In the classification offered (145) it should 

 be remembered that both friendly and competitive habits and 

 structures are always represented in the same individual. 



