32 INDIVIDUALITY OF MEMBERS OF SERIES, [introd. 



some maximum number, from which the formula characteristic of 

 each descendant has been derived by successive diminution. Here, 

 again, I do not doubt that many who employ this assumption 

 would hesitate to make it in set terms, but nevertheless it is the 

 logical basis of all such calculations. 



Now this hypothesis involves a definite conception of the 

 mode in which Variation works, and it is most important that 

 this should be realized clearly. For if it is true that each member 

 of a Series has in every form an individual and proper history, it 

 follows that if we had before us the whole line of ancestors from 

 which the form has sprung, we should then be able to see the 

 history of each member in the body of each of its progenitors. In 

 such a Series the rise of an individual member and the decline of 

 another should then be manifest. Each would have its individual 

 history just as a Fellowship in a College or a Canonry in a 

 Cathedral has an individual history, being handed on from one 

 holder to his successor, some being suppressed and others founded, 

 but none being merged into a common fund. In other words, 

 according to the received view of the nature of these homologies, 

 it is assumed that in Variation tlie individuality of each member 

 of a Meristic Series is respected. 



The difficulty in applying this principle is notorious, but when 

 the evidence of Variation is before us the cause of the difficulty 

 will become evident. For it will be found that though Variation 

 may sometimes respect individual homologies, yet this is by no 

 means a universal rule; and as a matter of fact in all cases of 

 Meristic Series, as to the Variation of which any considerable 

 body of evidence has been collected, numerous instances of Varia- 

 tion occur, in which what may be called the stereotyped or tra- 

 ditional individuality of the members is superseded. 



This error in the application of the principle of Homology to 

 individual members of Meristic Series has arisen almost entirely 

 through want of recognition of the unity of Meristic Repetition, 

 wherever found. In the case of a series of parts among which 

 there is no perceptible Differentiation, no one would propose to 

 look for individual Homologies. For example, no one consid* rs 

 that the individual segments in the intestinal region of the Earth- 

 worm have any fixed relations of this kind ; no one has proposed 

 to homologize single leaves of one tree with single leaves on 

 another ; it is not expected that the separate teeth of a Roach 

 have definite homologies with separate teeth of a Dace, for such 

 expectations would be plainly absurd. But in series whose mem- 

 bers are differentiated from each other the existence of such in- 

 dividuality is nevertheless assumed. To take only one case: a 

 whole literature has been devoted to tin- attempt to determine 

 some point in the vertebral column or in the spinal nerves from 

 which the homologies of the segments may bo reckoned. This is a 

 problem which in its several forms has been widely studied. Some 



