14 



SCIENCE 



[N. S. Vol. XXXI. No. 



the peripheral sense organs contains many 

 elements of no significance to the immedi- 

 ate capture of the quarry. These stimuli 

 the animal learns to ignore, perhaps in the 

 first instance unconsciously, by an applica- 

 tion of the biological law of habit; for 

 those reflex arcs which have adaptive value 

 in this particular situation will lead at 

 once to the desired eonsummatory reaction, 

 leave their permanent vestiges in the nerv- 

 ous system and so be more easily re- 

 peated, while the irrelevant stimuli do not 

 lead to a relief of the tension, come to 

 nothing and leave no such vestiges. Upon 

 later repetition of the series, the adaptive 

 stimuli find a more open path through the 

 nervovis system than the non-adaptive, and 

 accordingly they from the start tend to set 

 the direction of the nervous discharge 

 through the correlation centers, and dur- 

 ing this process the sense organs are re- 

 flexly adjusted to the sources of these 

 relevant stimuli to the exclusion of the ir- 

 relevant. This is the origin of attention. 



The analysis of other types of distance 

 reactions, such as avoidance of enemies, 

 search for mates, etc., would show for 

 them a similar significance for psycho- 

 genesis. The important point is that these 

 complex forms of distance reaction de- 

 mand for their highest efficiency greater 

 flexibility and modifiability of response 

 than do the visceral and contact reactions. 

 Here only is a high degree of intelligence 

 necessary. The cortex cerebri dominates 

 cerebral architecture only in mammals 

 where complex anticipatory reactions dom- 

 inate the behavior, and foresight, literal 

 and figurative, plays the leading role. 



The cerebral cortex is a correlation cen- 

 ter of a higher order, i. e., farther re- 

 moved from the primary sensori-motor 

 reflex arcs, than those of the brain stem. 

 It is not different in kind from those cen- 

 ters, but only in the extent of its removal 



physiologically from the primary centers 

 and the nature and complexity of the as- 

 sociational connections within it. In the 

 lower vertebrates the steps by which it has 

 been gradually lifted above the lower cor- 

 relation centers can now be traced with a 

 considerable degree of precision. Some of 

 this evidence will be reviewed in the sym- 

 posium on comparative neurology to be 

 held to-morrow in the meeting of the 

 Association of Anatomists. We have time 

 here merely to state in brief summary a 

 few salient features. 



We owe to the genius of Edinger the 

 suggestion that the earliest stages in the 

 origin of the peculiarities of the cerebral 

 hemispheres must be sought in a study of 

 the character of the reflexes connected 

 with the nose and lips, particularly the 

 feeding reactions. These have been termed 

 collectively the "oral sense" (Edinger) or 

 " Sclinuff elsinn" (Kappers) and may per- 

 haps best be called the muzzle reflexes. 



In lower vertebrates the sense organs of 

 the nose are probably the most impor- 

 tant receptors in the muzzle reflex com- 

 plex, and these are distance receptors and 

 not contact receptors. Accordingly, the 

 cerebral hemispheres were built up on the 

 basis of the olfactory correlation centers, 

 or rhinencephalon. In fishes, long before 

 we find a true cerebral cortex, ascending 

 tracts pass from the visceral sensory cen- 

 ters of the hypothalamus (probably mainly 

 gustatory in function) and from the so- 

 matic centers of the thalamus and mid- 

 brain (mainly tactile in function) to enter 

 the large forebrain correlation centers re- 

 lated to the olfactory apparatus. The as- 

 sociation of these sensory elements and 

 their return motor tracts produces the so- 

 called corpus striatum of fishes, an appa- 

 ratus which is probably largely concerned 

 with reflexes of the nose, lips and mouth. 



In Amphibia important optic projection 



