QQQ APPENDIX B. 



does not even mention. Had I never referred to the tongue-tip 

 at all, tlie various contrasts in discriminativeness which I have 

 named, between the one extreme of the forefinger-tip and the 

 other extreme of the middle of the back, would have abundantly- 

 sufficed to establish my case — would have sufficed to show the in- 

 adequacy of natural selection as a key and the adequacy of the 

 inheritance of acquired characters. 



It seems to me, then, that judgment must go against him by 

 default. Practically he leaves the matter standing just where 

 it did.* 



* While Professor Weismann lias not dealt with my argument derived 

 from the distribution of discriminativeness on the skin, it has been criticized 

 by Mr. McKeen Cattell, in the last number of Mind (October, 1893). His 

 general argument, vitiated by extreme misconceptions, I need not deal 

 with. He says : — " Whether changes acquired by the individual are 

 hereditary, and if so to what extent, is a question of great interest for ethics 

 no less than for biology. But Mr. Spencer's application of this doctrine 

 to account for the origin of species [!] simply begs the question. He 

 assumes useful variations [!] — whether of structure or habit is immaterial 

 — without attempting to explain their origin " : two absolute misstatements 

 in two sentences ! Ihe only part of Mr. Cattell's criticism requiring reply 

 is that which concerns the " sensation-areas " on the skin. He implies that 

 since Weber, experimental psychologists have practically set aside the 

 theory of sensation areas: showing, among other things, that relatively 

 great accuracy of discrimination can be quickly acquired by " increased 

 interest and attention. . . . Practice for a few minutes will double the 

 accuracy of discrimination, and practice on one side of the body is carried 

 over to the other." To me it seems manifest that " increased interest and 

 attention " will not enable a patient to discriminate two points where a few 

 minutes before he could perceive only one. That which he can really do 

 in this short time is to learn to discriminate between the massiveness of a 

 sensation produced by two points and the massiveness of that produced by 

 one, and to infer one point or two points accordingly. Respecting the 

 existence of sensation-areas marked off from one another, I may, in the 

 first place, remark that since the eye originates as a dermal sac, and since 

 its retina is a highly developed part of the sensitive surface at large, and 

 since the discriminative power of the retina depends on the division of it 

 into numerous rods and cones, each of which gives a separate sensation- 

 area, it would be strange were the discriminative power of the skin at large 

 achieved by mechanism fundamentally different. In the second place I 

 may remark that if Mr. Cattell will refer to Professor Gustav Retzius's 

 Biologische Untersuchungen^ New Series, vol. iv (Stockholm, 1892), he will 

 see elaborate diagrams of superficial nerve endings in various animals show- 

 ing many degrees of separateness. I guarded myself against being supposed 

 to think that the sensation-areas are sharply marked off from one another ; 

 and suggested, contrariwise, that probably the branching nerve-terminations 

 intruded among the branches of adjacent nerve-terminations. Here let me 

 add that the intrusion may vary greatly in extent ; and that where the intrud- 

 ing fibres run far among those of adjacent areas, the discriminativeness will 

 be but small, while it will be great in proportion as each set of branching 

 fibres is restricted more nearly to its own area. All the facts are explicable 

 on this supposition. 



