chap, xin.] DIGITS : LIZARD. 395 



digit, up to a condition somewhat resembling that of " double- 

 hand " in Man. If the first digit behind the hallux is the prae- 

 hallux, what are the digits on the tibio-tarsus ? If on the other 

 hand the appearance of an extra digit internal to the supposed 

 hallux is to be evidence that this " hallux " is the index, it may 

 equally be argued that if two digits come up internal to the 

 " hallux " then the supposed hallux is the medius, and so on inde- 

 finitely. Again, though with Howes and Hill we may accept 

 the cases of double-hallux as evidence that an extra digit may 

 appear by division of the hallux, which is indisputable, we must 

 equally accept the cases Nos. 597 and 598 as evidence that extra 

 digits may grow directly from the tarsus or even from the tibia, 

 though the hallux remain single and unchanged. And between 

 these two there is no line of distinction ; they pass into each 

 other. Do not these things suggest that we are looking for an 

 order that does not exist ? Is it not as if we should try to name 

 the branches of a tree in their sequences ? 



Possibly Continuous numerical Variation in Digits: miscellaneous 



examples. 



Under this heading are placed in connexion a few cases of 

 great interest. Whatever may be held as to the relation to the 

 problem of Species of the phenomena hitherto described, it can 

 scarcely be doubted that the following are instances of Variation 

 which at least may be of the kind by which new forms are evolved. 



Great interest would attach to a determination whether the 

 reduction of the digits iu these cases is a continuous or a discon- 

 tinuous process, but unfortunately these phenomena have been 

 statistically studied by no one, and it is not possible to do more 

 than make bare mention of the fact that such Variation is known 

 to occur. There is no statistical evidence as to whether the indivi- 

 duals in any one locality may not fall into groups, dimorphic or 

 polymorphic in respect of the degree to which the digits are 

 developed (compare the case of the Earwig, Introduction, p. 40). 

 As an inquiry into the Continuity of Variation such an investiga- 

 tion would be exceptionally valuable. In the case, for instance, of 

 Cistudo mentioned below, such a statistical inquiry should surely 

 not be hard to make. 



*I6. Chalcides. This is a genus of Lizards belonging to the 

 family Scincidse. In several genera of this family the limbs are 

 reduced or absent, differences in this respect being frequent among 

 species of the same genera. (See Boulenger, Catalogue of Lizards 

 in Brit. Mus., 1887, III. pp. 398, &c.) 



Mr Boulenger kindly shewed me a number of Lizards of the 

 genus CJialcides from the shores of the Mediterranean basin which 

 strongly resemble each other in colour and general appearance, but 

 which contained almost a complete series of conditions in respect 



