STATEMENT OF THE SUBJECT. 3 



carbonic acid, and give off oxygen, so essential to ani- 

 mals. All animals are developed from more or less 

 spherical eggs ; plants from seeds, or something analo- 

 gous to seeds ; and the mode of development, and the 

 extent to which growth goes on, are essentially different 

 in the two cases. 



It was stated above, that all animals are endowed with 

 sensation. Some, the lowest, have only general sensibil- 

 ity ; while others, and all the higher ones, are also en- 

 dowed with special kinds of sensation, called special 

 senses, of which there are five in number, the sense 

 of sight, of hearing, of smell, of taste, and of touch, 

 and dependent upon special organs. 



The natural divisions of the Animal Kingdom are 

 Branches or Types, Classes, Orders, Families, Genera, 

 and Species. That is, the animal kingdom is divided 

 into branches, each branch into classes, each class into 

 orders, each order into families, each family into genera, 

 each genus into species, the latter group being composed 

 of individuals essentially alike. These divisions are not 

 the contrivance of man, but exist in nature. According 

 to Agassiz, 



Branches are characterized by plan of structure, 



Classes, by the manner in which that plan is executed, 

 as far as ways and means are concerned, 



Orders, by the complication of that structure, 



Families, by form, 



Genera, by details of execution in special parts, 



Species, by the relation of individuals to one another, 

 and to the world in which they live, as well as by the 

 proportion of their parts, their ornamentation, &c. 



That is, certain characters determine the Branch, cer- 

 tain others determine the Class, others the Order, others 

 the Family, others the Genus, and others still the Spe- 

 cies. These principles of classification, however, are not 



