CHAP, xiv.] DIGITAL VARIETY AND SPECIES. 409 



Of actual variations from the arrangement of digits character- 

 istic of one form to that characteristic of another there are as yet 

 scarcely any examples. The cases given on pp. 395 to 398 being 

 the most evident. 



For the rest, that is to say examples of arrangements happen- 

 ing as variations matching no normal, some may say in haste that 

 with their like Zoology has no concern. It would be convenient if 

 those who make this careless answer (as many do) would mark 

 the point at which it is proposed to begin this rejection of the 

 evidence of Variation. Few perhaps realize how impossible it is to 

 give a real meaning to these distinctions. As regards digits, for 

 instance, I suppose that no one who holds the doctrine of Common 

 Descent would refuse to admit the evidence of Variation as to the 

 hallux of Hedgehogs (No. 612) as exemplifying the way in which 

 species may be built up — if indeed species are built up of varia- 

 tions at all. And if this case is admitted, by what criterion shall 

 we exclude cases of the formation of a hallux in the Dog ? But if 

 these are not excluded it is difficult to shew good reason for 

 not admitting the case of the three-phalanged digit placed as a 

 hallux in the Cat (No. 472) with all the curious series of which that 

 is only the first term. Are we quite sure that because there is no 

 Carnivore with a three-phalanged hallux therefore such a creature 

 could not exist in nature ? Still more difficult is it to shew cause 

 why duplicity of the hallux should be set apart as a variation not 

 capable of being perpetuated or of becoming part of the specific 

 characters of an animal, seeing that there is actual evidence both 

 in the case of the Dorking fowl and in the St Bernard clog that it 

 may become at least an imperfectly constant character. 



In connexion with the subject of this section many suggestions 

 with special bearing on particular cases, both positive and negative, 

 will strike every reader. In the present imperfect state of the evidence 

 it would be premature to pursue these. It may however be well to 

 mention that several writers, especially Joly and Lavocat (No. 554), 

 have seen in the cases of divided digit III in the Horse an indication 

 that the digit III of the Horse corresponds with the digits III and 

 IV of the Artiodactyles. The evidence as to syndactylism between 

 these two digits in Ox and Pig would probably be considered to 

 give support to the same view. But while we may note that the 

 relations of the digits with the carpus and tarsus of these forms, 

 were comparative evidence absent, should absolutely prevent any 

 one from seriously maintaining such an opinion, nevertheless the 

 fact that such closely similar systems of Symmetry may thus arise 

 independently of each other is of interest. 



