Individual Life, 51 



of life, such as secretion, motion, nervation, &c., for the 

 manifestation of which, special organs and tissues are set 

 apart, as explained in section iii. Organs are consequently 

 developed to fulfil these functions. The muscular or con- 

 tractile system subserves the function of motion ; some 

 parts are specially adapted to protect the more delicate 

 organs from external injury, whilst others are specially modi- 

 fied to act as a supporting framework to the same. More- 

 over, the nervous system with its accompanying sense organs, 

 is that which is especially differentiated to receive and 

 retain impressions from the external world, to regulate the 

 due performance of the functions of the other systems, and 

 generally, to instigate in the cells and tissues chemical changes 

 which result in the several phenomena we have already 

 considered. Lastly, it is necessary that certain organs 

 should be set apart for the removal of the bye-products of 

 the decomposition of complex compounds ; these may be 

 termed purificatory organs. Since it is manifest that the 

 bye-products must consist either of solid, fluid or gaseous con- 

 stituents, the purificatory organs will differ according as it is 

 their function to remove solid, fluid or gaseous bye-products. 

 The solid or fluid refuse matters are got rid of mainly by 

 the excretory or renal organs, whilst the gaseous bye-pro- 

 ducts are removed chiefly by the respiratory system. 



We have thus seen the individual to consist of a co- 

 ordinated series of organs, or systems, each performing its 

 own function, but all subservient to one end, viz. the proper 

 maintenance of individual life. 



We may arrange these organs and their functions in two 

 parallel columns, thus : 



Morphology (structure). Physiology (function). 



A. Nutritive or alimentary system. Nutrition. 



B. Circulatory ,, Circulation. 



C. Purificatory ,, Purification. 



i. Renal (fluid &c. excreta) i. Excretion, 



ii. Respiratory (gaseous &c. excreta) ii. Respiration. 



E 2 



