1903 Reptile Studies 301 



XI. The Limbs of Lizards. 1 



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 " serpenti- 

 form " is used to describe those lizards which are likewi-e 

 devoid of limbs, or partially so. 



The oldest reptiles were possessed of the ordinary number 

 of four limbs, constructed on the usual vertebrate 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 reduction 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 character in certain families and species. 

 The process is an excellent example of the origin of specific 

 characters which the field naturalist may well be expected 

 to be interested in, and we therefore propose to indicate 

 very simply and briefly the views that are held on the 

 subject, taking the slow-worm as an illustration. 



The problem may be thus stated. Seeing that the 

 earlier forms of reptiles were provided with limbs, and 

 that at the present time a large number are limbless, what 

 explanations does biology offer to account for this structural 

 change occurring in the first instance, and becoming a fixed 

 character afterwards in some species? Every field worker 

 should be familiar with modern teaching on this question, 

 and the group of lizards is a very convenient one in which 

 to indicate the views held by various schools of thought. 



For our purpose all that is necessary is to indicate the 

 two main lines on which the explanations of such problems 

 run, the older or Lamarckian view, and what we may 

 describe as the modern or Darwinian view. 



The underlying universal fact which has driven so many 

 observers to give their attention to these matters is the great 

 variation that is found everywhere in the animal world. The 



1 This article fnrnis chapter xiii, of Dr. Leighton's new book, British Li 



