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AN AMERICAN TEXT- BOOK OF PHYSIOLOGY. 



If the olfactory trad 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 



Pig. 1U.— Schema of the encephalon of a bony fish— embryonic i Edinger). The vertical black Hue marks 

 off the structures in front of the thalamus. 



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 contains the pathway for the impulses from the olfactory 

 bulbs to the cell-groups which control the cord. 



Fig. 115.— Schema of the encephalon of a cartilaginous fish ( Edinger). The vertical black line marks off 

 the striatum and pars olfactoria which lie in front of the thalamus. 



Passing next to the amphibia as represented by the (Vol;, there are several 

 series of observations on the physiological value <>f the divisions of the cen- 

 tral system. Schrader ' finds the following: Removal of the cerebral hemi- 

 spheres only, the optic thalami being uninjured, does not abolish the sponta- 

 neous activity of the frog. It jumps on the land or swims in the water, and 

 1 Archir fin- die (jemmmte Physiologie, 1S87, Bd. xli. 



