320 Till: Hl-X;iNNIN<;s OF CAI T SAL MORPHOLOGY 



" From such temporary changes are sharply to be dis- 

 tinguished all permanent alterations which first appear in 

 perceptible fashion through oft-repeated or long-continued, 

 enhanced functional activity. These produce a new and 

 lasting internal equilibrium of the organ, consisting in an 

 insertion of new molecules or a rearrangement of old. For 

 this reason they outlast the periods of functional form- 

 change, or, if as in the case of the muscles they them- 

 selves alter during functional activity, they regain their 

 state when the organ ceases to function" (p. 72, 1910). 

 " Oft-repeated exercise or heightened exercise of the 

 specific functions, or repeated action of the functional 

 stimuli which determine them, produces, as we have said 

 before, true form-changes as a by-product. These are of 

 two kinds. In so far as these form -changes facilitate 

 the repetition of the specific functions, I have called 

 them functional adaptntiotis. . . . Such as do not improve 

 the functioning of the organ are indeed by-products of 

 functioning, but without adaptive character ; they do not 

 belong to the class of functional adaptations at all" (p. 75, 

 1910). 



We may now enquire in what way functional adaptations 

 can arise as by-products of functioning. 



It is clear that natural selection in the sense of 

 individual or " personal " selection cannot adequately explain 

 the origin of functional structure and the functional harmony 

 of structure, for thousands of cells would have to vary 

 together in a purposive way before any real advantage 

 could be gained in the struggle for existence, and it is in the 

 highest degree unlikely that this should come about by 

 chance variation. 1 The development of purposive internal 

 structure is only to be explained by the properties of the 

 tissues concerned. 



In illustration and proof of the statement that functional 

 adaptation is due to the properties of the tissurs we may 

 adduce the development and regulation of the blood- 



1 Cf. the controversy between Herbert Spencer and Weismann on 

 the subject of " coadaptation " in the Contemporary Review for 1893 

 and 1894. See also YVeismann's paper in Darwin <uul Modern Science, 

 Cambridge, 1909. 



