PREFACE xiii 



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 which 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- 

 mits, are representative mammals, reptiles, amphibia, arthro- 

 pods, molluscs, worms, and ccelenterates. In many classes 

 there are students who can work faster than the others, or 

 who are interested in pursuing further their biological stud- 

 ies. Such students may be directed in carrying on some of 

 these studies either in class or outside of school hours. In 

 any case, students are likely to acquire considerable infor- 

 mation by reading these textbook descriptions and studying 

 the illustrations. 



All the work of the year should lead up to and culminate 

 in human biology. Here, too, however, many important top- 

 ics must be treated only superficially, or altogether omitted, 

 on account of lack of time. The authors believe that in 

 this, the most important part of the course, practical hygiene 

 should be taught as effectively as possible, and that the 

 necessity for good food, pure air, varied exercise, and suffi- 



