chap, xiii.] DIGITS : CAT. 313 



either at one of its ends (often associated with remodelling of 

 other members of the series) or in the middle of the series. 



Reduction in number of digits, or ectrodactylism as it is often 

 called, is usually so irregular in the manner of its occurrence that 

 little could be done as yet beyond a recitation of large numbers 

 of cases amongst which no system can be perceived. For the 

 present therefore the interest of these observations for the student 

 of Variation is comparatively small and they are for the most 

 part omitted. 



To the irregularity of ectrodactylism in general certain cases 

 of syndactylism are a marked exception and of these an account 

 will be given. 



After stating the morphological evidence as to numerical 

 Variation in digits in the several groups, reference will be made 

 to some collateral points of interest concerning such variations. 



There is a good deal of evidence respecting the recurrence 

 of digital variations in those lines of descent wherein they have 

 appeared. Facts of this kind have been frequently seen in the 

 case of Man, and other examples are known in the Cat, the Pig, 

 the Ox, Deer, Sheep, &c. References to these cases will be given. 



It will be seen that the facts contained in this section of 

 evidence are of consequence rather as indicating the limits set 

 on Variation, and from their bearing on the question of the nature 

 of Symmetry and of Homology, than from any more direct appli- 

 cation to the problem of Species, but even this cannot be said 

 with much confidence. 



There are in certain groups limbs such as the pes of Macro- 

 podidae or that of Peramelidae whose appearance forcibly recalls 

 what is seen in some teratological cases and the possibility that 

 they may have had such a sudden origin may well be kept in 



view 1 . 



Cat. 



The apprehension of the chief features in the evidence as to 

 digital variation in the Cat will be made more easy if a general 

 account of the subject be given as a preliminary. In order to 

 understand the peculiar phenomena seen in the limbs of poly- 

 dactyle cats certain points of normal structure are to be re- 

 membered. Of these the most important relate to the claws 

 and their disposition with regard to the second phalanx ; for it is 

 by this character that the relation of digits to the symmetry of 

 the limb may be determined. 



1 In the case named this is all the more likely from the circumstance that 

 according to Thomas, Cat. Marsup. Brit. Mus., p. 220, there is reason for supposing 

 that the extraordinary condition of the digits II and III was attained independently 

 in these two groups. 



