EELATION OF ANIMAL MOTION TO ANIMAL EVOLUTION. 357 



IV. 



It has been maintained above, that environmeut governs the 

 movements of animals, and that the movements of animals then 

 alter their environment. It has also been maintained that the 

 movements of animals have modified their structure so as to render 

 them more or less independent of their environment. The history 

 of animal life is in fact that of a succession of conquests over the 

 restraints imposed by physical surroundings. Man has attained 

 to a wonderful degree of emancipation from the iron bonds that 

 confine the lower organisms. 



It becomes then all important to examine into the elements in- 

 volved in animal movements. 



These are of the two classes, reflex and conscious. To the 

 former belongs the accelerated activity of muscular action and 

 circulation, inferred to have accompanied increase in the percent- 

 age of oxygen in the atmosphere, during the periods of geological 

 time. To the consciously performed acts belong all those due to 

 states of pain or pleasure in animals ; such as are excited by the 

 four classes of stimuli already mentioned. 



Doubtless physical changes in the surrounding medium have 

 always produced new reflex movements in animals, and have been 

 a first element in evolution. Such has been the immediate cause 

 of change of structure m plants, and in animals so far as they are 

 unconscious. But consciousness brings with it limitless possibili- 

 ties, since it places an animal in contact with innumerable stimuli 

 which leave unconscious beings unaffected. All the causes which 

 provoke the movements of higher animals are ajapeals to conscious- 

 ness, and the consequences due to movements of such beings have 

 only been possible through consciousness. 



It is evident then that sensibility to impressions has been the 

 prime essential to the acquisition of new movements, and hence 

 of new structure, other things being equal. Another essential, not 

 less important, has been memory ; because without this faculty, 

 experience, and hence education and the acquisition of habits of 

 movement, are not possible. 



The ascending development of the bodily structure in higher 

 animals has thus been, in all probability, a concomitant of the evo- 

 lution of mind, and the progress of the one has been dependent 

 in an alternating way on the progress of the other. The develop- 

 ment of mind has secured to animals the greatest degree of inde- 



