PREFACB. 5 



insects studied represent different families. By a comparison of 

 these insects we generalize and rise to the conception of an Order. 

 The next insects studied represent orders, and by a comparison of 

 their resemblances we proceed to the conception of a Class. The 

 table of differences enables us to frame a logical definition of each 

 order. The next animals studied represent not orders, but classes. 

 By a comparison of all these animals, we generalize and rise to the 

 conception of a Branch. The next animals studied represent 

 branches, and a similar process of the mind leads to the conception 

 of a Kingdom. 



It might be possible to use Vertebrates instead of Arthropods for 

 the purpose .of forming a conception of the less comprehensive 

 groups, but the inconvenience would be greater. Near the seashore 

 it might be possible to use MoUusks instead of Arthropods as the 

 beginning of the work, but certainly not with such satisfactory 

 assurances of success. 



Because of the importance of vertebrate dissection in the study 

 of human physiology, more attention is given to the Vertebrates 

 than is really demanded by the logical development of the plan. 

 The importance of Protozoa in the discussion of philosophic ques- 

 tions leads to a treatment of the subject seemingly inconsistent 

 with the rest of the book, but which it is believed will prove an 

 advantage to the users. 



Certain philosophic principles are discussed, when occasions 

 arise demanding their treatment, but nothing is touched upon that 

 does not grow directly out of the laboratory work. Such are the 

 topics of Protective Coloration, Mimicry, Protective Resemblance, 

 Vestigial Organs, von Baer's Principle, Homology of Parts, Meta- 

 morphosis, Variation, Development, Economic Effect, Parasitism, 

 Senses and Sense Organs. 



Enough work is suggested to occupy the time of a class one 

 period each day for one year of nine months. If a shorter time is 

 given to the study, the teacher may make a selection in one of two 

 waj's. He may lay the emphasis upon a smaller number of groups, 

 or upon a smaller number of animals in each group. According 

 to the second plan, a good selection would be to study only the 

 grasshopper, butterfly, beetle, housefly, crawfish, rabbit, clam, earth- 

 worm, starfish, hydra, sponge, paramoecium. The writer considers 

 it more advantageous to limit the study to Arthropods if the time 

 is very short. 



This book is the outcome of ten years' experience in teaching 



