750 OF THE FUNCTIONS OF THE NERVOUS SYSTEM. , 



manifested by Insects ; and it can scarcely be doubted by those who attentively 

 observe their habits that in such adaptations they are often guided by real 

 Intelligence. This must be the case, for example, when they make trial of 

 several means, and select that one which best answers the purpose; or when 

 they make an obvious improvement from year to year in the comforts of their 

 dwelling; or when they are influenced in the choice of a situation by peculiar 

 circumstances, which, in a state of nature, can scarcely be supposed to eifect 

 them. The complete domesticability of many Birds is in itself a proof of their 

 possessing a certain degree of intelligence ; but this alone does not indicate the 

 possession of more than a very low amount of it; since many of the most domes- 

 ticable animals are of the humblest intellectual capacity, and seem to become 

 attached to Man, principally as the source on which they depend for the supply 

 of their animal wants. But there are certain tribes of Birds, especially the 

 Parrots and their allies, which possess an extraordinary degree of editcabitity, 

 and which manifest a power of performing simple acts of reasoning, that are 

 quite comparable with those of a child when first learning to talk. This deve- 

 lopment of the Intelligence under the influence of Man, and in accordance with 

 his habits, rather than with the original habits of their species, is yet more re- 

 markable in the case of those Mammals whose instincts lead them to attach 

 themselves peculiarly to him, and whose powers of reasoning are called forth in 

 adapting themselves to the new circumstances in which they are thus placed. 

 The actions of a Dog, a Horse, or an Elephant are e'vidently the result, in many 

 instances, of a complex train of reasoning, differing in no essential respect from 

 that which Man would perform in similar circumstances ; so that the epithet, 

 "half-reasoning," commonly applied to these animals, does not express the whole 

 truth : for their mental processes are of the same kind with those of Man, and 

 differ more in the degree of control which the animal possesses over them than 

 they do in their own character. We have no evidence, however, that any of 

 the lower animals have a voluntary power of guiding, restraining, or accelerating 

 their mental operations, at all similar to that which Man possesses; these opera- 

 tions, indeed, seem to be of very much the same character as those which we 

 perform in our dreams, different trains of thought commencing as they are sug- 

 gested, and proceeding according to the usual laws, until some other disturb 

 them. Although it is customary to regard the Dog and the Elephant as the 

 most intelligent among the lower animals, it is not certain that we do so with 

 justice; for it is very possible that we are misled by that peculiar attachment 

 to Man, which in them must be termed an instinct, and which enters as a motive 

 into a large proportion of their actions; and that, if we were more acquainted 

 with the psychical characters of the higher Quadrumana, we should find in them a 

 greater degree of mental capability than we now attribute to them. One thing 

 is certain, that the higher the degree of intelligence which we find characteristic 

 of a particular race, the greater is the degree of variation which we meet with 

 in the characters of individuals; thus everybody knows that there are stupid 

 Dogs and clever Dogs, ill-tempered Dogs and good-tempered Dogs as there 

 are stupid Men and clever Men, ill-tempered Men and good-tempered Men. But 

 no one could distinguish between a stupid Bee and a clever Bee, or between a 

 good-tempered Wasp and an ill-tempered Wasp, simply because all their actions 

 are prompted by an unvarying instinct. 



782. In estimating the relative development of the Cerebrum in different 

 tribes of Animals, and in comparing this with their relative Intelligence, it 

 must be borne in mind that the size of the organ does not, considered alone, 

 afford a means of accurate judgment as to its power. For the quantity of vesi- 

 cular matter which it contains affords the only fair criterion of the latter; and 

 of this we must judge, not merely by the superficial area, but by the number 

 and depth of the convolutions, and by the thickness of the cortical layer. Again, 



