4 ZOOLOGY 



of the structure of parts of the individual, — as the organs and 

 systems of organs, the tissues, the cells. This is known as 

 gross anatomy if the study pertains to the larger units, — as 

 organs; it is called Histology, if the constituent elements of 

 these organs, as tissues and cells, are to be considered. 



Thus far we have thought of structure as stationary or per- 

 manent. As a matter of fact we know that each organism 

 begins life in a very modest way, as a single "cell," and grows 

 more complex by fairly well-defined stages until the adult con- 

 dition is reached. This is development. The science of 

 Embryology is the record of this history of the successive stages 

 which the individual animal 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 

 varities; 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 which live in the various bodies of water are 



