CHAPTER XIII 



THE LIMBS OF LIZARDS 

 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 



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