250 OUTLINES OF EVOLUTIONARY BIOLOGY 



evolved independently from more primitive pentadactyl types of 

 limb. 



We find analogous cases in other vertebrate groups. Several 

 of the lizards, such as the so-called slow worm or blind worm 

 (Fig. 105) and the " glass snakes " (Ophisaurus), have, by loss 

 of their limbs, come so closely to resemble snakes as to be 



FIG. 105. The Slow Worm, Anyuis frayilis, X J. (From a photograph.) 



indistinguishable by most people. The Coeciliidae (Fig. 106) 

 amongst amphibians, the Amphisbfenidae amongst lizards and 

 the Typhlopidae amongst snakes have all adapted themselves to a 

 burrowing underground life, like the earthworms. Their limbs 

 have completely disappeared, the body has become cylindrical and 

 worm-like and they have lost the use of their eyes, but though they 



FIG. 106. A worm-like, limbless Amphibian, Urm.typhlus africanus. (From 

 British Museum Guide.) 



have all come to resemble one another closely as the result of 

 convergent evolution they are not in reality at all nearly related. 

 The loss of limbs, the assumption of the worm-like form, &c., 

 have taken place quite independently in each group. 



The mammalian fauna of Australia consists mainly of members 

 of the single order Marsupialia or pouched mammals, but 

 different representatives of this order have come, by convergence, 

 to resemble closely members of widely different orders of 



