442 APPLIED BIOLOGY 



from tendons ; leather from the derails of the skin ; lean scraps 

 and blood are dried to make foods for poultry and other 

 animals ; bones are made into hundreds of useful articles and 

 the best small pieces are ground into bone-meal for feeding 

 poultry; and any particles of bone, blood, or flesh, not 

 usable in other ways, is dried and pulverized to make com- 

 mercial fertilizers for agricultural use. 



The dog was the first domesticated animal, and it is inter- 

 esting to note that primitive dogs were probably chiefly kept 

 as pets and companions, just as many of our modern dogs 

 are to-day. The development of such uses as hunting, guard- 

 ing flocks of sheep, and drawing sledges and carts seems to 

 have come after the dog's masters began to emerge from the 

 lowest barbarism. 



Among very injurious mammals are numerous species of 

 rodents (e.g., rats, mice, gophers, prairie-dogs, certain 

 squirrels, rabbits in Australia) ; some carnivors (e.g., the 

 dangerous cat-like species, the weasel-like forms, the bears 

 and wolves) ; and fruit-bats. 



Some mammals which are insect-eaters are indirectly bene- 

 ficial. Many bats, ant-eaters, and the moles are examples; 

 but owing to their subterranean habits the moles do much 

 damage to roots among which they burrow in search of larvae 

 of insects. 



References : Concerning the injurious mammals (rodents, 

 wolves, etc.) there are many pamphlets issued by the United 

 States Department of Agriculture. Two of the most inter- 

 esting books dealing with domesticated mammals are Shaler's 

 " Domesticated Animals," and J. G. Wood's " Dominion 

 of Man." 



LIFE-HISTORIES OF VERTEBRATES 



363. Embryology of Lower Vertebrates. The lesson on 

 development of the frog's x egg ( 56-63) should be reviewed 

 before continuing the study of the present chapter. 



