20 INTRODUCTION. 



and functions in our rapid sketch : and hasten to place before our 

 readers a view of the whole. 



The functions performed by animals may be brought into two 

 chief classes. One class comprises the vegetative, the other the 

 animal functions. The first are so called because they occur 

 equally in plants, and are also, on that account, called organic 

 functions. The last are peculiar to animals, and therefore are 

 called animal functions. 



To the organic functions belong Nutrition in the widest sense, 

 and Propagation. To nutrition belong three systems : namely, that 

 of Circulation, that of Assimilation, and that of Secretion. Respi- 

 ration is a part of the system of secretion : for the object of respi- 

 ration, like that of secretion, is the elimination of effete matter, its 

 volatilization, or its separation in a more fixed form : and both, in 

 this way, support that unceasing interchange of matter by which 

 the circle of vital phenomena is characterised. 



By means of these functions, which together are comprehended 

 by the name of Nutrition, the life of the individual is secured and 

 provided for. Other functions have reference to the life of the 

 species, and ensure its existence after the death of the individual. 

 These functions constitute Propagation, of which a part are dis- 

 charged by the male individual, viz. the secretion of the impreg- 

 nating fluid (semen), and its conveyance to germs capable oi 

 development. These germs are prepared and protected by the 

 female individual, and on the union of these functions depends the 

 being of the Embryo, the development of which is the final purpose 

 of propagation. 



To the animal functions also belong three systems : viz. the 

 nervous system, that of the organs of sense, and that of the organs 

 of motion. 



The food, when solid, is comminuted by means of the jaws and 

 teeth, or, when fluid, is imbibed. It is then conveyed into the in- 

 testinal canal, which ordinarily has an expansion called the stomach. 

 Here and at other parts of the intestinal canal different solvent 

 fluids are secreted for assisting the conversion of the food. The 

 nutrient part of the food is thus separated from the rest and taken 

 up by the surface of the inner wall of the canal consisting of 

 formative tissue : the remainder is rejected as unfit for the support 

 of the creature. 



