544 MAN CONTROLS HIS ENVIRONMENT FOR WEALTH 



injurious insects, and the little DeKajr snake feeds partly on slugs. 

 If it were not that the rattlesnake and copperhead are venomous, 

 they also could be said to be useful, for they devour English 

 sparrows, rats, mice, moles, and rabbits. 



Practical Exercises 23. Classify the animals mentioned in the preceding 

 sections as to direct or indirect economic importance. Add as much as you can 

 to the list. 



Make a list of all the ways in which animals living in your environment 

 help indirectly to make you comfortable. 



Food of herbivorous animals. We must not forget that other 

 animals besides insects and birds help to keep down the rapidly 

 growing weeds. Herbivorous animals the world over devour, 

 besides the grass which they eat, untold multitudes of weeds, 

 which, if unchecked, would drive out the useful plants of the 

 pastures, the grasses and grains. 



Self- Testing Exercise 



Animals furnish us with . (1), (2), (3), 



and (4) for clothing. Animal oils are obtained from the 



(5), (6), (7), and (8). Ivory is 



made from the (9) of QO) ; glue from (11) 



and (12) ; leather from the skins of (13), (14), 



and (15) ; perfumes from (16) (17) ; and 



pearls from (18). Coralis used for (19) (20). 



Sponges are (21) (22). The toad (23) 



(24). Most snakes are (25) to man. 



PROBLEM V. WHAT HARM IS DONE BY ANIMALS? 



Animals destructive to other animals used as food. Directly or 

 indirectly, animals, in their struggle for life, destroy quantities of 

 plants and other animals, that man uses as food. Starfish are 

 enormously destructive to young clams and oysters, as the follow- 

 ing evidence, collected by Professor A. D. Mead, of Brown Uni- 

 versity, shows : A single starfish was confined in an aquarium 

 with fifty-six young clams. The largest clam was about the 

 length of an arm of the starfish, the smallest about ten millimeters 

 in length. In six days every clam in the aquarium had been 



