Le cerveau comme un organe de l'esprit . perficial aswith aussi bien les structures plus profondes de la plus grande partie du corps, y compris tous les grands nerfs des membres inférieurs. Chap. II.] UN SYSTÈME NERVEUX. 53 ver-tehrates En plus, comme asBirds et Mam-mals, nous avons thissame fusion de gan-glie dans le spinalcord (fig. 19) whilsta processalso similaires, l'affiche-self à un moremarked point dans le cerveau. Dans thehigher andabove cette série de formulaires, tous dans Manhimself, le gan-glie du plus brainbecome,intégré et + et certains d'un enormousdevelopment theseparts takeon aussi. Le poids du cerveau entier,comme compa

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The brain as an organ of mind . perficial as well aswith the deeper structures of the greater part of the body, including all the great nerves of the limbs. Chap. II.] A NERVOUS SYSTEM. 53 In higher ver-tehrates, such asBirds and Mam-mals, we have thissame fusion of gan-glia in the spinalcord (fig. 19), whilsta similar processalso displays it-self to a moremarked extent inthe brain. In thehigher forms ofthis series, andabove all in Manhimself, the gan-glia of the brainbecome more andmore integrated, and some of theseparts also takeon an enormousdevelopment. The weight ofthe entire Brain, as compared withthat of the Spinal Cord indeed Un- ^^^ 20.—General view of Nervous System of Man, from . behind. 1, Cerebium ; 2, cerebellum ; 3, upper part of dergoes a great in- spiuaicord. (Mivart.)crease in each divi-sion of the vertebrates. In the Lamprey this relation issaid* to be as OlS to 1; in the Newt as 55 to 1; in thePigeon as 3*5 to 1; in the Mouse as 4 to 1 ; whilst in* Marshalls Outlines of Physiology, vol. i. p. 406.. 54 THE STRUCTURE OF A NERVOUS SYSTEM. Man it is about 40 to 1. Thus, whilst the Cerebrumand the Cerebellum, which together constitute the Brain, is actually much lighter in the Lamprey than the SpinalCord, these same parts in Man are found to attain com-paratively enormous dimensions, and greatly to exceed inweight the inferior, though highly important, spinalcentres. CHAPTEK in. THE USE AND NATURE OF SENSE ORGANS. Heat and light are physical influences to which eventhe lowest units of living matter respond, whether theirmode of life and nutrition be most akin to that of Plantsor to that of Animals. These influences act upon suchorganisms, either by stimulating, retarding, or otherwisemodifying the chemical changes occurring in their interior, and upon the existence of which their Life depends. Where the vital processes of the organism are stimulatedby these physical agencies, their incidence may, in manyinstances, become the cause of so-called * spontane

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