•sect, xiii.] INTRODUCTION. 71 



It would be interesting and I believe profitable to examine 

 somewhat further the curiously close analogy between the sym- 

 metry of bodily Division and that of certain mechanical systems 

 by which close imitations both of linear and of radial segmentation 

 can be produced ; and though to some this might seem overdaring, 

 the possibility that the mechanics of bodily Division are in their 

 visible form of an unsuspected simplicity is so far-reaching that it 

 would be well to use any means which may lead others to ex- 

 plore it. 



And even if at last this suggestion shall be found to have in it 

 no other element of truth, it would still be of use as a forcible 

 presentation of the fact, which when realized can hardly be 

 doubted, that among the factors which combine to form a living 

 body, the forces of Division may be distinguished as in their mani- 

 festations separable from the rest and forming a definite group. 

 For, already (Section V.) it has been pointed out that the patterns 

 of Division or Merism may be changed, while the Substance of the 

 tissues presents to our senses no difference. The recognition of 

 this essential distinctness of the Meristic forces will, I believe, be 

 found, to supply the base from which the mechanics of growth will 

 hereafter be attacked. 



The problems of Morphology will thus determine themselves 

 into problems in the physiology of Division, which must be 

 recognized together with Nutrition, Respiration and Metabolism, 

 as a fundamental property of living protoplasm. 



To sum up : there is a possibility that Meristic Division may 

 be a strictly mechanical phenomenon, and that the perfection 

 and Symmetry of the process, whether in type or in variety, may 

 be an expression of the fact that the forms of the type or of the 

 variety represent positions in which the forces of Division are 

 in a condition of Mechanical Stability. 



2. Possible nature of the Discontinuity of Substantive Variation. 



Passing from the phenomena of Division and arrangement to 

 those of constitution or substance we are, as has been said, again 

 presented with the phenomenon of discontinuous or total Varia- 

 tion, and we must seek for causes which may perhaps govern 

 and limit this totality, and in obedience to which the Variation 

 is thus definite. Now as in the case of Meristic Variation, by 

 arbitrarily limiting the examination to those cases which seem 

 the simplest it appears that there is at least an analogy be- 

 tween them and certain mechanical phenomena, bo by similarly 

 restricting ourselves to very simple cases there will be seen to 

 be a similar analogy between the discontinuity of some Sub- 

 stantive Variations and that of chemical discontinuity. It is 

 on the whole not unreasonable to expect that the definitem — 

 of at least some Substantive Variations depends ultimately on 

 the discontinuity of chemical affinities. To take but one instance, 



