PREFACE 



In the Preface to " Plant Biology " we discussed the general 

 point of view that we believed should be emphasized in a 

 course in elementary biology for students of high school age. 

 We there stated that in our judgment the primary emphasis 

 in the whole course should be placed on the many relations 

 of biology to human welfare. Many, of the experiments in 

 that volume, especially those relating to the chemical com- 

 position of lifeless and living things, the tests for the food 

 substances, and the principles of osmosis and of respiration, 

 apply equally well in the discussion of animal and human 

 biology. 



The method of presentation in " Animal Biology " is some- 

 what different from that employed in " Plant Biology," for 

 the reason that several widely different types of animals are 

 studied. Limitations of time compel a rigid and somewhat 

 narrow selection of groups for intensive study, and only those 

 functions of each animal are considered which have some 

 relation to human biology, or whjch have a broad, economic 

 bearing. Thus insects are discussed largely because of their 

 injurious or beneficial effects upon mankind ; birds and fishes, 

 because of their economic importance, and because of the 

 great need for their conservation; and one-celled animals 

 because of the light they throw on cellular processes. Certain 

 other somewhat less important topics are considered inci- 

 dentally ; for example, protective resemblance and metamor- 

 phosis among insects, and the striking adaptations of structure 

 to function in the bills, feet, and feathers of birds. 



The animals suggested for additional study, if time per- 



