ZOOLOGY. 



INTRODUCTION. 



Definition of the Subject. The science that 

 treats of organic nature, or living things, is termed Bi- 

 ology. It is divided into Botany, that treats of plants ; 

 and Zoology, that relates to animals. 



The Cell. All animals are made up of one or more 

 cells, minute globules of a jelly-like substance called 

 protoplasm, as a rule inclosed in a delicate covering or 

 membrane. The protoplasm of . genuine cells generally 

 contains minute moving granules, and a round transpar- 

 ent body termed the nucleus, that contains a dark ob- 

 ject, called the nucleolus. The lowest animals are single 

 cells, and are termed unicellular, but in the higher forms 

 the cells separate by self-division, and form two layers : 

 outer (ectoderm), inner (endoderm), while a middle layer 

 is called mesoderm. From these cell-layers bone and 

 muscular tissue are formed, and the animals are said to 

 be many-celled. 



Difference between Animals and Plants. It is 

 not difficult to distinguish between the higher forms of 

 animals and plants. The trees are sightless, have no 

 locomotive organs, and, as a rule, live upon inorganic 

 substances ; yet there are curious points of resemblance. 



