NERVOUS SYSTEM OF FISHES. 189 



developed and enormous eyes, we might, perhaps, gain some insight 

 into the office of the peculiar complexities of their large optic lobes : 

 without such experience, we can at best only indulge in vague 

 conjecture from the analogy of our own sensations. We find, when 

 Nature reduces the organs of sight to such minute specks as can 

 give but a feeble idea of the presence of light, sufficient, perhaps, to 

 warn the Amblyopsis to retreat to the darker recesses of its sub- 

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

 proportion, but retain a form and size, which, as compared with 

 their homologues 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 M. 

 Flourens (lxiv.), 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 prosencephalon were 

 special seats or organs of different psychical phenomena, such phe- 

 nomena 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 development of the homologues of the cerebral hemi- 

 spheres. Some species as, for example, the Shark and Pike, are pre- 

 datory and ferocious : some, as the Angler and the Skate, are crafty : 

 some, as the Sword-fish and Stickleback, 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 tlie brain 

 can hardly differ more in shape, in relative size, or in structure, 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 prosenccpliala of the Pike with those of the Carp, we 

 find them narrow in the devourer, broad in the prey. 



