CHAPTEK XIII 



THE LIMBS OF LIZAEDS 

 ORIGIN OF VARIATIONS ORIGIN OF A LIMBLESS LIZARD. 



The widespread idea that the slow-worm is a snake 

 and not a lizard is no doubt due to the fact that it 

 possesses no visible signs of the presence of limbs. 

 And as this absence of limbs is a characteristic feature 

 of the serpents, the term " serpentiform " is used to 

 describe those lizards which are likewise devoid of 

 limbs, or partially so. 



The oldest reptiles were possessed of the ordinary 

 number of four limbs, constructed on the usual verte- 

 brate pentadactyle type ; it is only among recent forms 

 that we meet with this singular departure from the 

 vertebrate type of limbs, of which we have such a 

 striking example in our indigenous slow-worm. In 

 other words, limbless lizards have been evolved from 

 lizards with four limbs, by a gradual process of reduc- 

 tion in size and number of limbs, and this reduction 

 having been specially suited to some of the conditions 

 in which reptiles are found, has become a fixed 



