42 COMPARATIVE PHYSIOLOGY. 



movement in. one direction renders that movement easier after- 

 ward, and in proportion to the frequency of repetition ; vrhich 

 is equivalent to saying that functional activity facilitates func- 

 tional activity. Once accepting this as of universal application 

 in biology, we have an explanation of the origin, the compara- 

 tive rigidity, and the necessity of habit. There must be a phys- 

 ical basis or correlative of all mental and moral habits, as well 

 as those that may be manifested during sleep, and so purely in- 

 dependent of the will and consciousness. We are brought, in 

 fact, to the habits of cells in considering those organs, and that 

 combination of structures which makes up the complex individ- 

 ual mammal. It is further apparent that if the cell can trans- 

 mit its nature as altered by its experiences at all, then habits 

 must be hereditary, which is known to be the case. 



Instincts seem to be but crystallized habits, the inherited 

 results of ages of functional activity in certain well-defined 

 directions. 



To a being with a highly developed moral nature like man, 

 the law of habit is one of great, even fearful significance. We 

 make to-day our to-morrow, and in the present we are deciding 

 the future of others, as our present has been made for us in part 

 by our ancestors. We shall not pursue the subject, which is of 

 boundless extent, further now, but these somewhat general 

 statements will be amplified and applied in future chapters. 



THE ORIGIN OF THE FORMS OF LIFE. 



It is a matter of common observation that animals originate 

 from like kinds, and plants from forms resembling themselves ; 

 while most carefully conducted experiments have failed to show 

 that living matter can under any circumstances known to us 

 arise from other than living matter. 



That in a former condition of the universe such may have 

 been the case has not been disproved, and seems to be the logical 

 outcome of the doctrine of evolution as applied to the universe 

 generally. 



By evolution is meant the derivation of more complex and 

 differentiated forms of matter from simpler and more homogene- 

 ous ones. When this theory is applied to organized or living 

 forms, it is termed organic evolution. There are two views of 

 the origin of life : the one, that each distinct group of plants 

 and animals was independently created ; whDe by " creation " is 



