4 ZOOLOGY. 



dition is reached. The science of Embryology is the record of 

 this history of the successive stages which the individual ani- 

 mal assumes in becoming adult, or at least until its organs are 

 essentially formed. 



7. In Physiology are considered the facts and laws relating 

 to the activities or functions of the organism and of its separate 

 parts. It includes the tracing back of the adult activities to 

 their lowest form, as found in the simplest animals or the 

 youngest stages of the higher animals. It includes the powers 

 of the single cell; the chemical and physical processes which 

 seem to underlie all the functional activities; the division and 

 more perfect performance of the primitive functions as the 

 various organs arise and come to do their special work. 

 Finally it includes the relation of the animal as a whole to other 

 animals of the same or of different species, to plants, and to 

 the inanimate surroundings. The term Ecology is applied to 

 this branch of physiology which treats of the relation of the 

 organism to the complex and wonderful conditions in which 

 it finds itself. Of recent years much emphasis is being given 

 to this branch of zoology. 



8. Animals may be studied as to their distribution or occur- 

 rence in the world. For example, we find lions in Africa and 

 Asia only, and the African and Asiatic lions are of different 

 varieties; the giraffe is found only in Africa; man is found 

 over the most of the habitable globe, but before the era of easy 

 communication between distant countries the men of different 

 regions were conspicuously different. Again we can easily see 

 that the animals that live in the various bodies of water are 

 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 distribution, or 

 geographical distribution. 



This is distribution in space. Similarly 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 



