12 



SCIENCE 



[N. S. Vol. XXXI. No. 784 



sensory centers, which sometimes attain to 

 enormous size, does not imply any more 

 highly developed psychic powers than 

 those of allied species with smaller brains; 

 but rather a higher elaboration of certain 

 reflex activities only. 



The same is in large measure true of cer- 

 tain suprasegmental or secondary correla- 

 tion centers. Thus, each one of the organs 

 of higher sense discharges its afferent im- 

 pulses into a massive primary receptive 

 center and this in turn transmits it to cor- 

 relation centers of the second, third and 

 higher orders, where these nerve impulses 

 are brought into relation with those from 

 other sense organs and with the appropri- 

 ate efferent pathways to the muscles or 

 other organs of response. The correlation 

 centers of this sort, which make up a large 

 part of the thalamus and midbrain, are 

 derivatives of the formatio reticularis tis- 

 sue and are functionally of the same type. 

 They permit of wonderfully complex dis- 

 criminative reactions and are more readily 

 modifiable by experience than are those 

 of the spinal cord and medulla oblongata. 



There is another type of highly devel- 

 oped correlation center whose psychic 

 value is still less than the sensori-motor 

 stations of which we have just been speak- 

 ing. I refer to the central mechanism of 

 what Sherrington calls the proprioceptive 

 system.* Of this the cerebellum is the 

 most important example. The chief func- 

 tion of this system being the coordination 

 and regulation of the skeletal musculature 

 and other organs of somatic response (as 

 distinguished from the interoceptive or 

 visceral effectors), it is naturally purely 

 reflex and its function is disturbed rather 

 than facilitated by voluntary interference. 



The correlation centers of the cerebral 



* On the relation of this system to the extero- 

 ceptive, see my article on the " Morphological 

 Subdivision of the Brain," Journal of Comparative 

 Neurology and Psychology, Vol. 18, 1908, p. 395. 



hemispheres occupy a unique position. 

 Their interpretation is possible only in the 

 light of their origin in the lower groups of 

 vertebrates. Numberless researches by 

 our most able anatomists and physiolo- 

 gists have accumulated a vast wealth of 

 data on this subject, which have, however, 

 stubbornly resisted correlation and inter- 

 pretation. Our debt to the generalizations 

 and luminous terminolog-y of Sherrington 

 appears on almost every page of this ad- 

 dress. Let us begin our inquiry into the 

 origin of cortical function with an exami- 

 nation of a typical feeding reaction. 



The primitive feeding reactions are very 

 simple reflexes, but even in the lowest ani- 

 mals they are easily modifiable, as Jennings 

 has shown for protozoa and Parker for sea 

 anemones. Predaceous species among the 

 lowly vertebrates commonly hesitate long 

 before they strike, but once the action is 

 initiated it follows to completion in a very 

 precise and invariable fashion. The pike 

 or the frog will watch the moving prey 

 long before the forward leap is made to 

 seize it ; but when once taken it will gener- 

 ally be swallowed at once whether it be a 

 living fly or an artificial one. 



Sherrington in discussing this reaction 

 divides it into an anticipatory phase — 

 fixation, coordination of somatic move- 

 ment for the leap and seizure — and a 

 consummatory reaction of mastication, 

 swallowing, etc. It is the latter alone 

 which gives satisfaction and in the interval 

 which elapses between the beginning of the 

 anticipatory reaction and the consumma- 

 tory reaction we shall find the key to the 

 problem of cortical function. 



The whole feeding reaction in the lowest 

 animals is so far as we can judge a blind 

 reflex; the consummatory phase is largely 

 so even in the highest animals, for once a 

 morsel is in the mouth the processes of 

 mastication and deglutition go on quite 

 automatically. 



