ORGANIC EVOLUTION — THE FACTORS 93 



properly be regarded as developmental, vary little or 

 not at all under stimulation ; muscle, as we see, normally 

 attains nearly the limits of its power to vary, as also do 

 healthy bone and cartilage ; while other structures, such 

 as skin, adipose tissue, and nervous tissue, do not 

 " normally " approach so nearly the limits of their powers 

 to vary. The skin thickens and hardens greatly in 

 response to the stimulation of intermittent pressure or of 

 moderate irritation, or it may expand immensely as over 

 tumours ; adipose tissue has a great power of growth ; 

 nervous tissue, judged by the function it performs, 

 whether of sensation, perception, thought, &c., has also 

 the power under continued stimulation of varying 

 very greatly beyond the normal limits. 



We may now ask ourselves the question — How much 

 of the tactual discriminativeness of the skin in various 

 parts of the body is due to direct inheritance, and how 

 much is individually acquired under the influence of 

 more or less continued stimulation ? The answer, I 

 think, must be, that while some of the discriminative- 

 ness is doubtless due to direct inheritance, — for in various 

 parts of the body where it is of particular importance 

 \e. g, hands and feet in man, tongue in some animals) are 

 found special nervous elements which subserve the 

 sense of touch, — yet beyond doubt much of it or most of 

 it is not due to direct inheritance, but to the power of 

 the individual organism to vary in correspondence with 

 the environment; the tactual discriminativeness being 

 most developed in those parts where it is oftenest 

 stimulated. In this way may be exjjlained all or most of 

 the superior discriminativeness of the front of the body 

 and the nose, as compared to the back of the body and 

 the lower part of the forehead respectively.^ 



1 Since writing tlie above I Lave come across the following 

 liaratfraph, whicli amply confirms the foregoing conclu.sion. 



" Mr. H., who in the fall of 1892 was the ' coach ' of a university 



