SECT. V.] INTRODUCTION. 23 



In the present Introduction I do not propose to forestall the 

 evidence more than is absolutely necessary for the purpose of 

 making clear the principles on which the facts are grouped, but 

 it will do the evidence no wrong if at the present stage it is stated 

 that Meristic Variation is frequently Discontinuous, and that in 

 the case of certain classes of Repetitions is perhaps always so. 



The nature of Merism and the manner in which Meristic 

 Variations occur will be fully illustrated hereafter, but it is 

 necessary to say this much at the present stage, since it is from 

 this Discontinuity in the occurrence of Meristic Variations that 

 the phenomena of Symmetry and Repetition derive their special 

 importance in the Study of Variation. 



The importance of the phenomena of Merism to the Study of 

 Variation is thus, in the first instance, a direct one, for the Varia- 

 tions which have resulted in the production of Meristic Systems 

 are a direct factor in Evolution. In addition to this direct relation 

 to the Study of Variation, the phenomena of Merism have also an 

 indirect relation, which is scarcely less important ; for they are a 

 factor in the estimation of the magnitude of the integral steps by 

 which Variation proceeds. This will be more evident after the 

 second group of Variations has been spoken of. 



We have thus far spoken only of the processes by which the 

 living body is divided into parts, and we have thus constituted a 

 group which is to include Variations in number, Division, and geo- 

 metrical position. From these phenomena of Division may be 

 distinguished Variations in the actual constitution or substance 

 of the parts themselves. To these Variations the name Substan- 

 tive will be given. Under this head several phenomena may be 

 temporarily grouped together, which with further knowledge will 

 doubtless be found to have no real connexion with each other. 

 For the present, however, it will be convenient to constitute such 

 a temporary group in order to bring out the relative distinctness of 

 Variations which are Meristic. 



These two classes of Variation, Meristic and Substantive, may 

 be recognized at the outset of the study. There can be no doubt 

 that they are essentially distinct from each other, and the proof 

 that they are thus distinct will be found in the evidence of Varia- 

 tion, for it will be seen that either may occur independently of the 

 other. An appreciation -of this distinction is a first step towards 

 a comprehension of the processes by which the bodies of organisms 

 are evolved. 



A few simple illustrations may make the nature of these two 

 classes of Variations more clear. For example, then, the fiower of 

 a Narcissus is commonly divided into six parts, but through 

 Meristic Variation it may be divided into seven parts or into only 

 four. Nevertheless there is in such a case no perceptible change 



