486 THE POPULAR SCIENCE MONTHLY. 



"afford a glaring example of taking the unessential in place of the essential, and 

 drawing conclusions from a partial and altogether insufficient survey of the phe- 

 nomena. For this ' tactual discriminativeness,' which is alone dealt with by Mr. 

 Spencer, forms the least important, and probably only an incidental portion of the 

 great vital phenomenon of skin-sensitiveness, which is at once the watchman and 

 the shield of the organism against imminent external dangers " (Fortnightly Re- 

 view, April, 1893, p. 497). 



Here Mr. Wallace assumes it to be self-evident that skin-sensi- 

 tiveness is due to natural selection, and assumes that this must be 

 admitted by me. He supposes it is only the unequal distribution 

 of skin-discriminativeness which I contend is not thus accounted 

 for. But I deny that either the general sensitiveness or the special 

 sensitiveness results from natural selection ; and I have years ago 

 justified the first disbelief, as I have recently the second. In The 

 Factors of Organic Evolution, pp. 66-70, I have given various 

 reasons for inferring that the genesis of the nervous system can 

 not be due to survival of the fittest ; but that it is due to the direct 

 effects of converse between the surface and the environment ; and 

 that thus only is to be explained the strange fact that the nervous 

 centers are originally superficial, and migrate inward during de- 

 velopment. These conclusions I have, in the essay Mr. Wallace 

 criticises, upheld by the evidence which blind boys and skilled 

 compositors furnish ; proving, as this does, that increased nervous 

 development is peripherally initiated. Mr. Wallace's belief that 

 skin-sensitiveness arose by natural selection is unsupported by a 

 single fact. He assumes that it must have been so produced be- 

 cause it is all-important to self-preservation. My belief that it is 

 directly initiated by converse with the environment is supported 

 by facts ; and I have given proof that the assigned cause is now 

 in operation. Am I called upon to abandon my own supported 

 belief and accept Mr. Wallace's unsupported belief ? I think not. 

 Referring to my argument concerning blind cave animals, 

 Prof. Lankester, in Nature of February 3, 1893, writes : 



" Mr. Spencer shows that the saving of ponderable material in the suppression 

 of an eye is but a small economy : he loses sight ot the fact, however, that pos- 

 sibly, or even probably, the saving of the organism in the reduction of an eye to a 

 rudimentary state is not to be measured by mere bulk, but by the non-expenditure 

 of special materials and special activities which are concerned in the production 

 of an organ so peculiar and elaborate as is the vertebrate eye." 



It seems to me that a supposition is here made to do duty as a 

 fact ; and that I might with equal propriety say that " possibly, or 

 even probably/' the vertebrate eye is physiologically cheap : its 

 optical part, constituting nearly its whole bulk, consisting of a low 

 order of tissue. There is, indeed, strong reason for considering it 

 physiologically cheap. If any one remembers how relatively 

 enormous are the eyes of a fish just out of the egg a pair of eyes 



