CHAPTER V. 



VERTEBRATA. 



PHYSIOLOGY — HISTOLOGY — BOUNDARY BETWEEN THE TWO KINGDOMS— CELL 

 DEVELOPMENT — GROWTH OF TISSUES — SKIN, CARTILAGE, TEETH, 



BONE, ETC. 



most complicated state in which 

 matter exists, is where, under 

 the influence of life, it forms 

 bodies with a curious internal 

 structure of tubes and cavities, 

 in which fluids are moving and 



:j ■f 



producing incessant internal 

 changes. These are called orga- 

 nised bodies, because of the 

 various organs which they contain, and 

 they form two remarkable classes ; those 

 of the lowest class are for the most part 

 fixed to the soil, and are recognised as 

 vegetables, — the structure of these we have 

 already considered ; those of the higher 

 order are endowed with power of locomo- 

 tion, and are called animals. Some of the peculiarities 

 and minute structure of the invertebrate animals have 

 already been made the subject of investigation, and we 

 now propose to extend our observations to the vertebrate. 

 The study of the Science of Life, or the building up of 

 the living structure, is termed Physiology, or Biology ; 1 

 and that part of it more particularly relating to the minute 

 structure of the organs of animals has been termed 

 Histology.' 2 



(1) From fltos, life, and \oyos, discourse— a. discourse on life ; a riore expres- 

 sive term than physiology. 



(2) From Io-tus, a tissue, or web, and \o-vur, a discourse. 



