CHAP. I.] OF A NERVOUS SYSTEM. 13 



the upper parts of the alimentary canal before thn morsel 

 that has been captured can be swallowed. A series of 

 movements of this kind may occur in response to some 

 touch upon the external surface of such an organism ; 

 and, after a rudimentary sense of sight has once been 

 established, impressions produced by an object not in con- 

 tact may lead to complex locomotions in pursuit, followed 

 by others for capture, and others again for the swallowing 

 of food or prey. The sight of a different object may, how- 

 ever, lead to movements of flight rather than to those 

 of pursuit. The organism may hasten away, to avoid a pos- 

 sible attack since in the past this kind of experience may 

 often have followed the appearance of a similar object. 



Again, the process of digestion in such animal organ- 

 isms is aided by certain accessory glandular organs, whose 

 activity is stimulated by the contact of food with different 

 portions of the alimentary canal. Absorption of the pro- 

 ducts of digestion is either simple and direct from the 

 alimentary canal into some general body-cavity whose 

 fluid comes into contact with most of the organs ; or it 

 takes place through definite channels, and empties itself 

 into a circulatory system proper in which blood is pro- 

 pelled throughout the body by means of a contractile 

 heart containing one or more chambers. Glands also 

 exist whose office it is to modify the constitution of the 

 blood. There may be either gills or lungs to renovate 

 it by contact with oxygen and to get rid of effete products 

 though in this latter .function the organs of respiration 

 are powerfully aided by renal and other emunctories. 



All these are functions having to do with the preserva- 

 tion of the life of the individual, though another set of 

 activities also come into play in animals that have attained 

 a grade of organization of the kind to which we are refer- 

 ring. These new activities pertain to the sexual function 



