420 MERISTIC VARIATION. [part i. 



to all. Yet even if, as now seems likely, the 4-jointed tarsus 

 be not a congenital variation but is rather a result of regenera- 

 tion, there is still difficulty in reconciling the now established 

 fact that the form of the regenerated part, though different from 

 the normal, is scarcely less constant, with any hypothesis that 

 the constancy of the normal is dependent upon Selection. 



If it were true that the smallness of the mean variation of the 



t 1 ..." 



ratio y , which is ultimately the measure of the constancy and 

 Li 



truth to type of the 5-jointed tarsus, is really due to Selection 

 and to the comparative prosperity of specimens whose tarsal pro- 

 portions departed little from the normal, to what may we ascribe 



T l 



the smallness of the mean variation of the ratio -j- ? Are we 



to suppose that the accuracy of the proportions of the regenerated 

 tarsus is due to the Natural Selection of individuals which in 

 renewing their tarsi conformed to this one pattern ? 



We are told that the struggle for existence determines every 

 detail of sculpture or proportions with such precision that in- 

 dividuals which fall short in the least respect are at a disad- 

 vantage so great as to be capable of being felt in the struggle, 

 and so decided as to lead to definite and sensible effects in Evolu- 

 tion. If this is so, should we not expect that individuals which 

 had suffered such a comparatively serious disadvantage as the 

 loss of a leg or of a tarsus, would be in a plight so hopeless that 

 even though some of them may survive, renew the limb and 

 even breed, yet, as a class, by reason of their mutilation they 

 must rank with the unfit ? Nevertheless we find not only that 

 there is a mechanism for renewing the limb, but that the renewal 

 is performed in a highly peculiar way ; that in fact the structure 

 newly produced differs from the normal just as species differs 

 from species, and is scarcely less true and constant in its pro- 

 portions than the normal itself. 



Now if this exactness in the proportions of the renewed limb 

 is due to Selection, it must be due to Selection working among 

 the mutilated alone ; and of them only among such as re- 

 newed the limb ; and of them only among such as bred. 

 Moreover if the accuracy of the form of the renewed tarsus is 

 due to Selection working on fortuitous variations in the method 

 of renewal, and not to any natural definiteness of the variations, 

 the number of selections postulated is already enormous. But 

 this vast number of selections must by hypothesis have all been 

 made from amongst the mutilated — a group of individuals that 

 would be supposed to be at a hopeless disadvantage 1 . 



1 The same dilemma is presented in all cases where a special mechanism or 

 device exists (and must be supposed to have been evolved) only in connexion with 

 regeneration. An instance is to be seen in the Lobster's antenna. As is well known 

 the antennary filament of the Lobster when lost is renewed not as a straight out- 



