ENCEPHALON OF FISHES. 289 



the presence of light, sufficient, perhaps, to warn the Ambly- 

 opsis to retreat to the darker recesses of its subterranean 

 abode, that the optic lobes are not reduced in the same proportion, 

 but retain a form and size, which, as compared with their homo- 

 logues in other animals, are sufficiently remarkable to suggest a 

 function over and above that of receiving the impressions of 

 visual spectra, and forming the ideas consequent thereon. 



The anatomical condition of the prosencephalon, and its 

 homology with the hemispheres of the bird's brain, experimented 

 on by Flourens, 1 would lead to the belief that it was in this 

 division of the fish's brain that impressions become sensations, and 

 that here was the seat of distinct and tenable ideas : of such, for 

 example, as teach the fish its safest lurking-places, and give it that 

 degree of caution and discernment which requires the skill of the 

 practised angler to overmatch. If different parts of the prosence- 

 phalonwere special seats or organs of different psychical phenomena, 

 such phenomena are sufficiently diversified in the class of Fishes, 

 and are so energetically and exclusively manifested, as to justify the 

 expectation, on that physiological hypothesis, of corresponding 

 modifications in the form and developement of the homologues of 

 the cerebral hemispheres. Some species, as, for example, the 

 Shark and Pike, are predatory and ferocious : some, as the Angler 

 and the Skate, are crafty : some, as the Sword-fish and Stickle- 

 back, are combative : some, as the Carp and Barbel, are peaceful, 

 timid browsers : many fishes are social, especially at the season 

 of oviposition : a few are monogamous and copulate ; still fewer 

 nidificate and incubate their ova. 



Now, if we compare the prosencephala of the Shark and Pike, 

 fishes equally sanguinary and insatiable, alike unsociable, the 

 tyrants respectively of the sea and lake, we find that those parts 

 of the brain differ more in shape, in relative size, and in struc- 

 ture, than in any two fishes. The prosencephalon of the Pike 

 is less than the cerebellum, much less than the optic lobes ; in 

 the Shark it exceeds in size all the rest of the brain : in the Pike, 

 the prosencephalon consists of two distinct lobes brought into 

 communication only by a slender transverse commissure ; in the 

 Shark, the hemispheres are indistinguishably blended into one 

 large subglobular mass. If we compare the prosencephala of the 

 Pike with those of the Carp, we find them narrow in the de- 

 vourer, broad in the prey. 



The Lophius lurks at the bottom, hidden in the sand, waiting, 

 like the Skate, for its prey to come within the reach of its jaws : 



1 LXIV. 



VOL. I. U 



