120 NATURAL SCIENCE. February, 



olfactory apparatus only : it is merely a centre for olfactory 

 associations. The differences between a fish and a reptile must be 

 that the latter is able to store, associate and compare its olfactory 

 impressions — the former, not. In passing up the animal scale new- 

 centres are added, one at a time, and so piece by piece the whole 

 cerebral cortex is built up. It is for the future to trace the details of 

 the process, but already we can follow the " installation," as it were, 

 of the cortical visual field. In fishes, in young animals, in a new-born 

 child, the retinal fibres end in the roof of the mid-brain. In the 

 second month, as the child begins to acquire visual experience, fibres 

 develop from the mid-brain to the occipital region of the cerebrum, 

 and other anatomical connections quickly arise between this cortical 

 visual field and other regions of the brain. The child now begins not 

 merely to see, but to perceive and correlate visual impressions. This 

 visual tract from the mid-brain to the cortex is wholly absent in lower 

 vertebrates. Fishes are readily deceived by the angler ; even a 

 hungry frog or snake may fail to see its prey unless the latter moves, 

 or is detected by smell. But birds have this tract well developed, and 

 they clearly perceive and store impressions. It takes a good 

 scarecrow to deceive a sparrow. Just as the lower vertebrate depends 

 on smell for the supply of its requirements, so the bird relies on vision. 

 It is of course amongst mammals that the cerebral cortex acquires its 

 chief complexity, and that the manifold development of association 

 tracts gives rise to the white substance of the hemispheres. 



The bearings of Professor Edinger's question will now be more 

 clearly grasped. The animal kingdom got on for a long while without 

 a cerebral cortex : What capacities are possible to the lower primary 

 centres unaided ? What, in the domain of a smell, can a reptile accom- 

 plish more than a fish ? What, in the domain of vision, can a bird 

 do which a reptile cannot ? What new faculties has a mammal 

 associated with the new cortical areas which it possesses ? Even in 

 man we require accurate topographical studies of individual brains in 

 relation to individual gifts and faculties. It is evident that in the 

 answers to such questions as these, psychology may attain a far more 

 secure basis than any which has yet been provided for it. 



The particular case put by Dr. Edinger is this : There is a 

 general opinion, that fish have some sort of memory, that they can 

 recognize people, know how to find or to avoid places, where they 

 have formerly had some experience ; that fish, which have once 

 escaped the rod, know the bait, etc. It is highly desirable that all 

 observations of this kind should be collected in the interest of com- 

 parative psychology. The reason is that till now we believed the 

 function of memory to depend on the action of the brain-cortex. All 

 experience in man and in the higher animals has led to that con- 

 clusion. But it has in recent years been proved that fish have no 

 brain-cortex at all ; they are the only existing vertebrates without 

 one. Now, if we could prove beyond the possibility of doubt, that 



