INTRODUCTION 5 



very different from those living on the land ; those in the frigid 

 zones are different from those in the temperate and torrid. 

 All such topics are treated under the head of Zoogeography, or 

 geographical distribution. This is distribution in space. 



The hard parts of animals are found as fossils in many of 

 the surface rocks of the earth. The various systems of rock- 

 strata are characterized by more or less different fossil remains, 

 indicating a variation in the animal life during the successive 

 periods of the earth's history. This distribution of animals 

 in time is the subject-matter of Palcsozoology. The facts 

 of palseozoology and the conclusions resting thereon are 

 among the most important in the whole realm of Zoology, 

 inasmuch as they supplement the facts gained from the study 

 of embryology and morphology of living species, thus enabling 

 the investigator to trace the history of the various races ol 

 animals into the remote past. In this way we also learn much 

 of the history of the earth itself. 



9. Practical Exercises. — The student may submit a written report on the dis- 

 tribution of the animals in his immediate neighborhood, based on his own observa- 

 tions. The report need not be exhaustive in order to convince the student of the 

 effect of the environment, which includes everything in the surroundings, on the 

 distribution of animals. Some classification should be made of the varieties of 

 territory included; — as river, pond, lowland, woodland, prairie, mountain, and the 

 like. Determine, by reference to the authorities available, the geographical 

 distribution of the following: the elephant, the camel, the kangaroo, the horse, 

 the white bear, the seal, the salmon, the crocodile, the reef-forming coral, the 

 sponge of commerce. Select and find the distribution of five other species having 

 a personal interest to you. 



10. Classification. — In studying animals and plants one is 

 soon impressed with the fact that among the thousands of 

 individuals, even of the same general kind, there are no two 

 exactly alike; and yet among them all, with their manifest dif- 

 ferences, there are numerous points of similarity. These two 

 facts make it possible to group those most alike into more or 

 less coherent classes, separating them at the same time from 

 other classes. The forming, naming, and defining of these 

 groups and subgroups we call Taxonomy or Classification. 

 Manifestly, true classification must depend upon the facts de- 

 rived from the completest possible study of the structure and 

 relations of organisms, and can only be perfect when we know 



