2 JO STUDIES IN THE EVOLUTION OF ANIMALS 



may have been a good protection, if the animal squatted and 

 hid himself under his huge dish-cover ; in other instances, how- 

 ever, this same protection might have become a source of great 

 weakness. Let us suppose that the Glyptodont, as is likely, was 

 sometimes wholly unarmoured on his abdominal surface, like 

 many of the existing Armadillos. Then if his more active enemies 

 had learnt to upset him, and leave him kicking in the air like 

 an overturned Turtle, he would be wholly at their mercy, and they 

 might eat his underside, and scoop him out at leisure, in spite 

 of his formidable dorsal protection. We need not even suppose 

 that each of his enemies required to have great strength, for we 

 know that several Grampuses attack a Whale at the same time 

 and kill it, and that Wolves co-operate in their attacks on large 

 animals. 



Such is a speculative sketch of the physical conditions which 

 possibly may have brought about the existing active and smaller 

 races of animals. Briefly, the hugeness of the endo- and exo- 

 skeletons of those ancient extinct monsters may have been due to 

 excess of lime in their food. 



I have called the absence of lime-stiffening in the exo-skeleton 

 a rachitic skin. It is not unlike a rachitic egg-skin, when the hen is 

 unable to obtain lime salts for building up the egg-shell. In the 

 latter case, the deficiency is a great disadvantage, but in the former 

 an elastic and flexible skin, giving freedom to the movements of 

 the muscles and endo-skeleton, would have been a great advan- 

 tage. 



Concurrently with the loss of armour, and with the development 

 of muscular activity, there must have been evolved a larger and more 

 complicated brain. Those huge monsters of ancient times are 

 known to have had tiny brains, in proportion to their prodigious size. 

 The spinal cord no doubt supplemented the small size of the 



