192 STUDIES IN THE EVOLUTION OF ANIMALS 



plates proper on its abdominal surface, but, on its chest and 

 between its hind legs, it has the merest varnish of former scales. 

 They are not unlike in nature to the black dabs on the lips of 

 S err anus Gigas, after the scales of the latter have thinned out into 

 nothing. The spots on the middle part of the abdomen of this 

 Tatusia are less distinct. 



Armour on the abdominal surface of the Armadillo would 

 evidently have been inconvenient to an animal that rolls itself up 

 into a ball, and shows its armoured back to the enemy. It seems 

 that the Tatusia lost its abdominal plates, because they had become 

 not only useless, but inconvenient, or perhaps from some other 

 cause ; it, however, retained their vestiges as spots. The alternative 

 supposition would be that the Tatusia took to rolling itself up, 

 when it began to lose the stiff plating on its abdominal surface, 

 while the dorsal armour divided itself into moveable sections, which 

 admitted of its rolling itself up. 



However this may have been, it is clear that the Armadillo 

 descended from an ancestor which was armoured both dorsally and 

 ventrally, somewhat in the way shown in Fig. 73. It is stated 

 that certain Glyptodonts had an armour on their ventral side, which 

 suggests that of the Turtle. 



The existing Crocodiles have retained their bony dorsal plating, 

 while the ventral armour is made up of hard horny plates. In the 

 Crocodile, each plate is surrounded by skin, and its movements are 

 much freer than could have been those of the Glyptodon. 



I would now ask what business has the Peba Armadillo with 

 spots on its under surface, supposing them to have been originated 

 by a simple process of natural selection^ The spots on the 

 abdominal surface could in no sense harmonise with their surround- 

 ings, and so become protective, for, when this Armadillo is un- 

 folded, and moving about, its abdomen is close to the ground, and 



