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AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



hemispheres (including the corpora striata as well as the mantle) be removed, 

 the animal apparently suffers little inconvenience. The movements are undis- 

 turbed ; such fish play together in the usual manner, discriminate between a 

 worm and a bit of string, and among a series of colored wafers to which they 

 rise, always select the red ones first. 1 In these fish the eye is the controlling 

 sense-organ, and, as will be recognized (see Fig. 199), the operation has by no 

 means damaged the primary centres of vision. 



Quite different is the result when the cerebrum is removed from a shark. 2 

 In this case, although the eyes are intact, the animal is reduced to complete 

 quiescence ; yet on the whole, the nervous system of the shark is rather less 

 well organized and more simple than that of the bony fish. The astonishing 

 effect produced is explained by a second experiment (see Fig. 200). If the 



FIG. 200. Schema of the encephalon of a cartilaginous fish (Edinger). The vertical black line marks 

 off the striatum and pars olfactorius, which lie in front of the thalamus. 



olfactory tract be severed on one side, no marked disturbance in the reactions 

 of the shark is to be noticed ; when, however, both tracts are severed, the 

 shark acts as though deprived of its cerebrum. From this it appears that 

 the removal of the principal sense-organ, that of smell, is the real key to the 

 reactions, and that the responsiveness of the fish is reduced in the first instance, 

 because in this case it has been deprived of the impulses coming through the 

 principal organs of sense, and in the second the removal of the cerebrum is 

 mainly important because the cerebrum contains the pathway for the impulses 

 from the olfactory bulbs to the cell-groups which control the cord. 



Passing next to the amphibia as represented by the frog, there are several 

 series of observations on the physiological value of the divisions of the central 

 system. Schrader 3 finds the following : Removal of the cerebral hemispheres 

 only, the optic thalami being uninjured, does not abolish the spontaneous activ- 

 ity of the frog. It jumps on the land or swims in the water, and changes from 

 one to the other without special stimulation. It hibernates like a normal frog, 

 retains its sexual instincts, and can feed by catching passing insects, such as flies 



1 Steiner : Die Functionen der Centralnervensystems, 1888. 2 Steiner, loc cit. 



3 Archiv fur die gesammte Physiologic, 1887, Bd. xli. 



