420 M ERISTIC VARIATION. OAKT i. 



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

 I..- not a congenital variation but is rather a result of regenera- 

 tion, there i-; .-till difficulty in reconciling the now established 

 t'ai-t that tli'' till-in of the regenerated part, though different from 

 tin- normal, i> >carce]y less constant, with any hypothesis that 

 th- constancy i.t' tin- normal is dependent upon Selection. 



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



f> 



ratio , which is ultimately the measure of the constancy and 

 I . 



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

 and t>i hi- comparative prosperity of specimens whose tarsal pro- 

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



T 1 

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



bo suppose that the accuracy of the proportions of the regenerated 

 tarsus is due to the Natural Selection of individuals which in 

 tin ir tarsi conformed to this one pattern ? 



\\V an- 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. It' this is so, should we not expect that individuals which 

 had sut'ti'ivd 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 

 musl 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 it' 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- 

 ni'wed 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 detiniteness of the variations, 

 the number of selections postulated is already enormous. But 

 this \a.-t nunilier <>f selections must by hypothesis have all been 

 made from amongst the mutilated a group of individuals that 

 would be suppose -i I to be at a hopeless disadvantage 1 . 



1 The same dilemma is presented in nil cases win-re a special mechanism or 

 device exists (and must lie supposed to have beeu evolved) only in connexion with 



Deration. An in tain-,- i- to he seen in the Loh-tei 's antenna. As is well known 

 [In- antennai y tilainriit of the Lobster when lost is rein-wed not as a str<ii<iltt out- 



