36 SUBSTANTIVE VARIATION : EXAMPLES. [introd. 



possibility that the resemblance between the two sides of a 

 bilaterally symmetrical body may be in some essentials the same 

 as the resemblance between offspring of the same parent, or to 

 use an inclusive expression, that the resemblance between the 

 members of a Meristic Series may be essentially the same as the 

 resemblance and relationship between the members of one family ; 

 that the members of a row of teeth in the jaw, of a row of peas 

 in a pod, of a chain of Salps, or even a litter of pigs, all resulting 

 alike from the processes of Division, may stand to each other 

 in relationships which though different in degree may be the 

 same in kind. 



If reason shall appear hereafter for holding any such view as 

 this, the result to the Study of Biology will be profound. For 

 if it shall ever be possible to solve the problem of Symmetry, 

 which may well be a mechanical one, we shall thus have laid a 

 sure foundation from which to attack the higher problem of 

 Variation, and the road through the mystery of Species may thus 

 be found in the facts of Symmetry. 



SECTION VIII. 

 Discontinuity in Substantive Variation: Size. 



From the subject of Merism and the thoughts which it suggests, 

 we now pass to another matter. The first limitation by which we 

 proposed to group Variations was found in the characters which 

 they affect : the second relates to the magnitude, or as I shall call 

 it, the Continuity of the variations themselves. And though 

 for many a conception has no value till it be cast in some finite 

 mould, my aim will be rather to describe than to define the 

 meaning of the term Continuity as applied to Variation. In 

 dealing with a subject of this obscurity, where the outlines are 

 doubtful, an exact mapping of the facts cannot be made and 

 ought not to be attempted; but I trust that from the present 

 indications, vague though they are, some larger and more definite 

 conception of Discontinuity in Variation may shape itself hereafter 

 by a process of natural growth. For this reason I shall as far as 

 possible avail myself of examples rather than of general expres- 

 sions, whether inclusive or exclusive. 



To those who have studied the recent works of Galton, the 

 conceptions here outlined will be familiar. In the chapter on 

 " Organic Stability " in Natural Inheritance, the matter has been 

 set forth with charming lucidity, and what follows will serve 

 chiefly to illustrate the manner in which the facts of Natural 

 History correspond with the suggestions there made. 



In the ease of most species it is a matter of common knowledge 



