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guarding the physical seats of sensation, emotion, and thought. The inspection 

 of vertebrate forms shows the necessity for this provision in the increasing 

 complexity and delicacy of the Nervous Apparatus, and in its greater import- 

 ance relatively to the entire Organism. Bearing in mind that the Nervous 

 System of Insects is capable of two great divisions, viz. : (1) the ganglions of 

 the trunk with their double connecting cord, (2) the ganglia of the Head ; we 

 find in the Vertebrata that there are gradually developed two additional nervous 

 centres, both contained in the skull. These are called the cerebellum and 

 cerebrum. So that in vertebrates we may take a general view of the system 

 of nervous centres as comprising (1) the spinal cord with its extensions ; (2) the 

 sensory ganglia, or nervous organs of the special senses of sight, hearing, 

 and smell and pei'haps of gener-al tactile sensibility ; which, collectively, may be 

 called the Sensorium ; (3) the cerebellum ; (4) the cerebrum. The first two, you 

 will recollect, and those only, have their analogues in the Insects and higher 

 Molluscs. From the fact that the greatest proportionate development of sensory 

 ganglia occurs in those tribes of living creatures, I mean the social insects, in 

 which instinct is most powerful, Physiologists infer, no doubt justly, that the 

 physical seat of instinct is in that part of the frame. Now there is, in com- 

 parative Physiology, without calling in the aid of other sciences, the very 

 strongest ground for a similar inference respecting the physical seat of intelli- 

 gence as distinguished from instinct. For, as we pass from one type of 

 vertebrated animal to another we find that the intelligence of the species 

 appears to increase in a just ratio with the increase in the size of the cerebrum; 

 and this organ also becomes, at every step upwards, more and more complex 

 in structure. The inference of course is, that the cerebrum is the physical 

 organ of intelligence. Of the cerebellum the functions seem to be to some 

 extent unascertained. Tt is largest in man, and appears to be a necessary 

 accompaniment of the expanding powers of the cerebrum. It is generally 

 considered as enabling us unconsciously to combine and harmonise the efforts 

 of a great variety of muscles in complex actions, in obedience to a general 

 volition. We have all seen how a complicated piece of music may be per- 

 formed automatically, if the piece be well known to the performer ; although 

 in learning the piece each movement might have required the exertion of the 

 will. The direction of this sort of automatic action seems to be one, at least, 

 of the functions of the cerebellum, acting in conjunction with the sensory 

 ganglia. 



Returning to the structure of the Cerebrum : it is divided into two sec- 

 tions, known as the Cerebral Hemispheres. The Hemispheres occupy quite a 

 subordinate position in the lower classes of Vertebrates — that is in Fishes and 

 Reptiles. Looking, from above, at the brain of a Cod-fish, the sensory ganglia, 

 especially those pertaining to the Organs of Sight and Smell, are very promi- 

 nent objects, and form the chief mass of the brain. Gradually, as we rise in 

 the scale, the Cerebral Hemispheres assume increased importance, till in the 

 Mammalia they form the mass of the brain, capping and completely covering 

 in the sensory ganglia, and also, more or less, over-lapping the Cerebellum. 



The Cerebellum partly shows itself, however, when we look at the brain 

 from above downwards, in every creature except man himself, and those 

 animals which, in general structure, make a close approach to the Human 

 type — -I mean, of course, the Monkeys, Baboons, and Apes. In all these 

 animals the posterior lobe of the Cerebrum is well developed, and completely 

 covers the Cerebellum when the brain is viewed from above. So closely, indeed, 

 does the brain of some of the higher Ajies approach to that of man, that Professor 

 Huxley declares it to be impossible " to erect any Cerebral barrier " between 

 them. "So far as Cerebral structure goes it is clear," he says, "that man 

 differs less from the Chimpanzee or the Orang than these do even from the 



