ADAPTATIONS 115 



considerable size ; but in Lialis burtoni they are reduced to 

 minute almost imperceptible filaments. It will not fail to be 

 noticed that the Pygopodidce differ from Chirotes, the one genus 

 of the Amphisbcenidce with vestigial limbs, in the retention of 

 remnants of the hind instead of the front pair. Although 

 nothing definite appears to have been ascertained with regard 

 to the habits of these " scale-footed " lizards, it may be inferred 

 from this difference that they are not burrowing. 



The last group that has to be noticed from the present 

 point of view is that of the skink-lizards (Scincidcz) and certain 

 allied types. A large number of skinks are lizards of ordinary 

 form, although they often show a marked tendency to elonga- 

 tion of the body. In certain species of the genera Clialcides 

 and Lygosoma, which habitually dwell in sandy situations and 

 have burrowing habits, this elongation of the body becomes es- 

 pecially noticeable, and is accompanied by a tendency to the 

 loss of the limbs. These skinks seem, indeed, to be actually 

 on their way towards the assumption of a snake-like form and 

 habit, and it has been suggested that certain differences in the 

 degree of development of the limbs upon which specific dis- 

 tinctions have been founded, are really due to individual varia- 

 tion, the species being in this respect in a state of unstable 

 equilibrium. Be this as it may, in the common sand-skink 

 {Chalcides ocellatus) the five toes are fully developed ; in C. 

 mionecton they are reduced to four; while in C. lineatus and C. 

 tridactylus only three digits remain, while the fore-limbs are 

 only about a quarter of an inch long in specimens measuring 

 ten inches in length, although the hind pair is somewhat more 

 developed. Lygosoma lineo-punctulatum may be taken as an 

 example of a species in which the digits are represented by a 

 pair of toes, looking much like the pincers of a lobster. 

 Finally, in Chalcides guentheri of Palestine, which is very 

 similar to C. tridactylus but has the length of the body in- 

 creased to fourteen inches, the limbs are reduced to stumps, 

 without trace of their component digits. One step further on 

 the same line of evolution, and we should have a snake-like 

 skink. 



As a matter of fact, such a type is represented by the 

 members of the so-called family Anelytropidce, such as Anely- 

 tropsis papillosus of Mexico, and Typhlosaurus and Feylinia in 



