PREFACE. v ii 



an inland student, having got the typical idea of an insect 

 from the study of a common grasshopper, for example, is 

 much better prepared to understand the general structure 

 of the Crustacea, though he may never have seen the few 

 forms peculiar to fresh water. In the same way after 

 having studied the common earthworm, he can form a 

 better idea of the complicated structure of many marine 

 worms, though these he may never see. After long delib- 

 eration, and some hesitancy, the author is forced to depart 

 from common usage, and present, in this first book, only a 

 few of the leading groups in the animal kingdom. 



From the abundance of material, and the comparative 

 ease with which the specimens may be preserved for cabinet 

 use, shells and insects have always formed the favorite col- 

 lections of children. They are the most common objects in 

 nearly all collections, and it has seemed to the author that 

 here the pupil ought to commence his studies. 



Having learned to collect and prepare specimens for the 

 cabinet, and to observe the relations and differences existing 

 among them, the pupil is then prepared to go on to forms 

 less familiar, or to study in detail the material already gone 

 over. 



Great pains have been taken to present, in every case, 

 drawings made from the animal, expressly for this book. 

 They are all American, and, with few exceptions, are en- 



