INTRODUCTION. xxix 



capybara ; among the Insectivora it is as 1 to 60 in the little two-toed ant-eater, but 

 is as 1 to 500 in the great ant-eater. The brain of a porpoise four feet long may- 

 weigh 1 lb. avoirdupois ; that of a whale (BaioBnoptera) 100 feet in length does not 

 exceed 4 lbs. avoirdupois ; in Quadrumana the brain of the Midas marmoset is to the 

 body as 1 to 20 ; in the gorilla it is as 1 to 200. 



" But such ratios do not show the grade of cerebral organization in the mammalian 

 class; that in the kangaroo is higher than that in the bird, though the brain of a 

 sparrow be much larger in proportional size to the body : and the kangaroo's brain is 

 superior in superficial folding and extent of gray cerebral surface to that of the 

 petaurist. The brain of the elephant bears a less proportion to the body than that of 

 opossums, mice, and proboscidian shrews, but it is more complex in structure, more 

 convolute in surface, and with proportions of pros- to mes-encephalon much more 

 nearly than in the human brain. The like remark applies to all the other instances 

 above cited." Owen explains these facts by saying that the brain grows more rapidly 

 than the body, and is larger in proportion thereto at birth than at full growth ; " so 

 in the degree in which a species retains the immature character of dwarfishness, the 

 braii*is relatively larger to the body." 



The bearing of the facts known as to the relative size of the brain and the convolu- 

 tions are thus discussed by Bastian : " There cannot therefore be, among animals of 

 the same order, any simple or definite relation between the degree of the intelligence 

 of the creature and the number or disposition of its cerebral convolutions — since this 

 structural feature of the brain seems to be most powerfully regulated by the mere bulk 

 of the creature to which it belongs." It fails still more, when comparing representa- 

 tives of different orders. For example, the beaver's brain is almost smooth, while that 

 of the sheep has numerous convolutions, which both in number and complexity decid- 

 edly surpass even those of the dog. Yet among closely related animals and those of 

 about the same size, especially in species of the same genus, or, as in the case of man, 

 in individuals of the same species, we may look for some proportional relations between 

 the development of their cerebral convolutions and their intelligence. 



" Size of brain, and with it convolutional complexity, must," Bastian remarks, " be 

 closely related to the number and variety of an animal's sensorial impressions, and also 

 to its power of moving continually or with great energy. 



"The importance of taking into account the powers of movement possessed 

 by the animal is fully borne out by the fact that the brain attains such a remarkable 

 size in the shark, as well as in the porpoise and the dolphin — all of them creatures 

 whose movements are exceptionally rapid, continuous, and varied. The great increase 

 in the size of the cerebellum in each of these creatures is, therefore, not so surprising ; 

 but it seems very puzzling, at first sight, to understand why this should be accompanied 

 by a co-ordinate increase in the development of the cerebral hemispheres. For this, 

 however, there are two causes, the one general and the other more special. It is a fact 

 generally observed, that sensorial activity, and therefore intelligent discrimination, in- 

 creases with an animal's powers of movement ; and secondly, there must be special 

 parts of the cerebral hemispheres devoted to the mere sensory appreciation of move- 

 ments executed. The nerve elements lying at the basis of this latter appreciation, 

 however they may be distributed through the hemisphei-es, would naturally be the 

 more developed (and, consequently, all the more calculated to help to swell the size of 

 the cerebrum), in proportion to the variety and continuance of the movements which 

 the animal is accustomed to execute." 



