July 4, 1902.] 



SCIENCE. 



the debate in favor of the view that the 

 objective world is real? 



Consciousness is not only screened from 

 the objective world from which it receives 

 all its sensations, but also equally from im- 

 mediate knowledge of the body through 

 which it acts. As I write this sentence I 

 utilize vaso-motor nerves, regulating the 

 cerebral blood currents, and other nerves 

 which make my hand muscles contract and 

 relax, but of all this physiological work 

 my consciousness knows nothing though it 

 commands the work to be done. The con- 

 tents of consciousness are as unlike what is 

 borne out from it as they are unlike what 

 is borne in to it. 



The peculiar untruthfulness to the ob- 

 jective which consciousness exhibits in 

 what it gets and gives would be perplexing 

 were it not that we have learned to recog- 

 nize in consciousness a device .to secure 

 better adjustment to external reality. For 

 this service the system of symbols is success- 

 ful, and we have no ground for supposing 

 that the service would be better if con- 

 sciousness possessed direct images or copies 

 instead of symbols of the objective world. 



Our sensory and motor* organs are the 

 servants of consciousness; its messengers 

 or scouts; its agents or laborers; and the 

 nervous system is its administrative office. 

 A large part of our anatomical character- 

 istics exist for the purpose of increasing 

 the resources of consciousness, so that it 

 may do its bionomic function with greater 

 efficiency. Our eyes, ears, taste, etc., are 

 valuable, because they supply conscious- 

 ness •with data ; our nerves, muscles, bones, 

 etc., are valuable, because they enable con- 

 sciousness to effect the needed reactions. 



Let us now turn our attention to the 

 problem of consciousness in animals. The 

 comparative method has an importance in 

 hiology which it has in no other science, 



* And other organs in efferent relations to 

 consciousness. 



for life exists in many forms which we 

 commonly call species. Species, as I once 

 heard it stated, differ from one another 

 with resemblance. The difference which 

 resembles we term an homology. Our 

 arm, the bird's wing, the lizard's front 

 leg are homologous.. The conception of 

 homology both of structure and of func- 

 tion lies at the basis of all biological sci- 

 ence, which must be and remain incompre- 

 hensible to any mind not thoroughly im- 

 bued with this conception. Only those 

 who are deficient in this respect can fail 

 to understand that the evidence is over- 

 whelming that animals have a conscious- 

 ness homologous with the human conscious- 

 ness. The proof is conclusive. As re- 

 gards at least mammals— I think we could 

 safely say as regards vertebrates— the 

 proof is the whole sum of our knowledge 

 of the structure, functions and life of 

 these animals. 



As we descend the animal scale to' lower 

 forms there is no break and therefore no 

 point in the descent where we can say here 

 animal consciousness ends, and animals be- 

 low are without it. It seems inevitable 

 therefore to admit that consciousness ex- 

 tends far down through the animal king- 

 dom, certainly at least as far down as there 

 are animals with sense organs or even the 

 most rudimentary nervous system. It is 

 unsatisfactory to rely chiefly on the ana- 

 tomical evidence for the answer to our 

 query. "We await eagerly results from 

 psychological experiments on the lower in- 

 vertebrates. A sense organ however im- 

 plies consciousness, and since such organs 

 occur among coelenterates we are led to 

 assign consciousness to these animals. 



The series of considerations which we 

 have had before us lead directly to the con- 

 clusion that the development and improve- 

 ment of consciousness has been the most 

 important, really the dominant, factor in 

 the evolution of the animal series. The 



