124 MOUNTAIN AND MOORLAND 



except the burrowers have got a single row of large 

 scales on the ventral surface of the body; these grip 

 the ground when they are raised by the under-skin 

 muscles, and they enable the ribs, moving backward 

 and forward, to row the body along. In the Slow 

 Worm the body is covered almost uniformly with 

 roundish overlapping scales, with small bony plates 

 beneath them, which are never found in Snakes. Al- 

 though the creature is often called a Blind Worm 

 (which does not say much for observation), it has well- 

 developed eyes, with yellowish-red iris and with mov- 

 able lids, whereas in Snakes the upper and lower lids 

 are mere vestiges, and the third eyelid seems to have 

 bcome fixed as a transparent blind across the non- 

 movable eye. Thus the Slow Worm has not the 

 rt stare " of the Snake. Moreover, although the open- 

 ing of the ear is a very small pit in the Slow Worm, 

 there is an opening, which is more than can be said 

 of Snakes. Finally, if a Slow Worm is a foot long, 

 about half of this is tail, whereas that part of a Snake's 

 body is comparatively short. Internally, the two kinds 

 of reptiles are not in the least like one another. We 

 have given part of the answer, then, to the very 

 reasonable question: Why is a Slow Worm not a 

 Snake ? a question which is not a conundrum, but a 

 useful enquiry into the differences separating two 

 creatures which are superficially a little like one 

 another, having been similarly adapted to similar 

 conditions of life. This kind of adaptive resemblance 

 is often called " convergence." 



The colour of the Slow Worm is variable, but on 

 the whole it is brownish above and darker below. 

 The newborn young ones are silvery above, with three 



