io6 



ZOOLOGY. 



by reason of these facts, more and more likely in succeeding 

 generations to possess those habits and structures suiting them 



to their surroundings. 



FIG. 50. 



FIG. 50. Young Opossum (Didelphys rirginiana) photographed 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 pre- 

 hensile? What are the habits of the opossum? How is this species dis- 

 tributed on the earth? Where are other marsupials found? 



143. Practical Exercises. Find other instances which seem to indicate 

 adaptation either in structure or habit to special features in the environ- 

 ment : as adaptations to prevent undue evaporation in a dry climate ; 

 adaptations to warm conditions ; to drouth ; to the use of special plants 

 as food ; to light ; to gravity. Illustrate from observation and by library 

 reference the types of adaptations cited in the text above. Is the power 

 of sleeping an adaptation of any value ? Among what animals is it found ? 

 Find instances in which useful adaptations have become useless and even 

 hurtful from changed conditions of life. 



