598 APPENDIX A. 



The necessary antagonism of Individuation and Reproduction 

 does indeed show itself amongst the higher animals, in some 

 degree in the manner hitherto traced ; namely, as determining 

 the total bulk. Though the parts now thrown off, being no 

 longer segments or gemmae, are not obvious diminutions of the 

 parent, yet they must be really such. Under the form of in- 

 ternal fission, the separative tendency is as much opposed to the 

 aggregative tendency as ever ; and, other things equal, the greater 

 or less development of the individual depends upon the less or 

 greater production of new individuals or germs of new indi- 

 viduals. As in groups of cells, and series of groups of cells, we 

 saw that there was in each species a limit, passing which, the 

 germ product would not remain united ; so in each species of 

 higher animal there is a limit, passing which, the process of cell- 

 multiplication results in the throwing off of cells, instead of re- 

 sulting in the formation of more tissue. Hence, taking an aver- 

 age view, we see why the smaller animals so soon arrive at a 

 reproductive age, and produce large and frequent broods ; and 

 why, conversely, increased size is accompanied by retarded and 

 diminished fertility. 



But, as above implied, it is not so much to the bulk of the 

 body as a whole, as to the bulk of the nervous system, that 

 fertility stands related amongst the higher animals. Probably, 

 indeed, it stands thus related in all cases ; the difference simply 

 arising from the fact, that whereas in the lower organisms, where 

 the nervous system is not concentrated, its bulk varies as the 

 bulk of the body, in the higher organisms it does not do so. Be 

 this as it may, however, we see clearly that, amongst the verte- 

 brata, the bodily development is not the determining circum- 

 stance. In a fish, a reptile, a bird, and a mammal cf the same 

 weight, there is nothing like equality of fecundity. Cattle and 

 horses, arriving as they do so soon at a reproductive age, are 

 much more prolific than the human race, at the same time that 

 they are much larger. And whilst, again, the difference in size 

 between the elephant and man is far greater, their respective 

 powers of multiplication are less unlike. Looking in these cases 

 at the nervous systems, however, we find no such discrepancy. 

 On learning that the average ratio of the brain to the body is 

 in fishes, 1 to 5668 ; in reptiles, 1 to 1321 ; in birds, 1 to 212 ; 

 and in mammals, 1 to 186 ; * their different degrees of fecundity 

 are accounted for. Though an ox will outweigh half-a-dozen 

 men, yet its brain and spinal cord are far less than those of one 

 man ; and though in bodily development the elephant so im- 

 mensely exceeds the human being, yet the elephant's cerebro- 

 spinal system is o'nly thrice the size attained by that of civilized 

 * Quain's Elements of Anatomy, p. 672. 



