CHAPTER V. 



VERTEBRATA. ANIMAL STRUCTURE. 



PHYSIOLOGY HISTOLOGY CELL THEORY GEOWTH OF TISSUES SPECIAL 

 TISSUES SKIN, CAETILAGE, TEETH, BOSE, ETC. 



( HE 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 

 f producing incessant internal 

 change," says the philosophic 

 Dr. Arnott. These are calied 

 organised bodies, because of the 

 various organs which they con- 

 . tain, and they form two remarkable 

 classes ; the individuals of the lowest class 

 are fixed to the soil, and are recognised as 

 vegetables, the structure of these we have 

 already considered; the individuals of the 



higher order are endowed with power of 



locomotion, and are called animals : it is 

 some of the peculiarities and minute structure of the 

 latter that we are now about to examine. The phe- 

 nomena of growth, decay, death, sensation, self-motion, 

 and many others, belong to animal life; but, from occurring 

 all in material structures, which subsist in obedience to the 

 laws of physics and chemistry, life is truly a super- 

 structure on these two, and cannot be studied indepen- 

 dently of them. Indeed, the greater part of the pheno- 

 mena of life are chemical and physical phenomena, modified 

 by an important additional principle. The phenomena of 

 life, from thus involving generally the agency of all the 



