27-1 dk(;k\ki;atiox in limcs of li/.auds. 



Discussiox. 



There is no reason to question that tlie throe species of 

 Chaniaesaura, or the originals of the stock from which they came, 

 were at one time more conformable to the usual plan of structure 

 of the Lacertilia, that is, were possessed of larger pentadactyl 

 limbs and of a tail more nearly of the same length as the body. 

 Further, it would be in harmony with the usually accepted inter- 

 pretation of evolutionary zoology to regard the three species as 

 representing a successional series in the process of limb degenera- 

 tion : first, a general diminution in size without the loss of any 

 of the parts; second, the orderly loss of the first and fifth digits 

 and later of the fourth and second, followed by the corresponding 

 metacarpals and metatarsals and elements of the carpus and 

 tarsus; and, finally, the complete degeneration of the limb as a 

 whole. All the available stages would be regarded as so many 

 steps, one following upon another, in the gradual loss of the limbs. 

 If a larger number of individuals were procurable a continuous 

 series could in all probability be arranged, showing all the stages 

 from the pentadactylous condition to the tridactylous, didactylous 

 and monodactylous, to a condition of complete absence, thereby 

 adding another to the many examples already elaborated and 

 accepted as evidence of continuous or determinate variation. 



Apart from the possible influence of selection, however, there 

 appear to be no experimental observations which afford any 

 support for such successional changes taking place in nature. 

 Mutational changes, so far as we know them, are haphazard and 

 disconnected, and probably never constitute a continuous series 

 in any one direction. Hence there seems to be little or no experi- 

 mental proof in support of continuous or determinate evolution, 

 even though results in comparative anatomy and palaeontology 

 call insistently for it. 



How then are we to regard the facts as here presented? It 

 is manifest that in the genus Cluunaesaura, as in other well- 

 known genera of the Lacertilia — A7}guis, Ophisauvus, Tctra- 

 dactylus^the germinal factors concerned with limb production 

 are, or have been in the past, in a highly mutative state ; and, as 

 a result, we have the many departures from the normal limb 

 condition characteristic of the lizards. It by no means follows, 

 however, that the mutative changes of the limb factors would 

 always be of the same degree, nor express themselves exactly in 

 the same fashion; and this variability, combined with subsequent 

 intermingling, may well have produced the many stages occurring 

 within the various genera. Without calling for an orderly 

 succession of germinal changes, we may conceive that in the case 

 of Cliatnacsnuva different and independent factorial changes, along 

 with the later combinations resulting from inter-breeding, have 

 given us the different stages in limb degeneration which we now 

 possess. Eeduction in size of limb, as we know it m C. acnca, 

 may have occurred as a single mutation ; the reduction in size and 

 the varying losses of the digits may also have occurred in C. 

 anguina as independent separate mutations, and apart from the 



