LOSS OF CALCAREOUS ARMOUR IN MAMMALS 209 



allied races. If Buffbn had known of the gigantic Sloth and 

 Armadillo-like animals, and of the lost Pachydermata, he might 

 have said with greater semblance of truth that the creative force 

 in America had lost its power rather than it had never possessed 

 great vigour.' 



What is the reason of this change from the monstrous-sized 

 animals of the past to their modern pigmy descendants ? With- 

 out carbonate of lime, neither the external nor the internal 

 skeletons can be built up. The same cause want of sufficient 

 carbonate of lime in the waters, plants, etc. that caused the 

 rachitis of the dermal skeleton, prevented the internal skeleton 

 from attaining a great size ; hence the pigmy animals of these 

 days, as compared with the monsters of those days. But let us 

 not fancy that it was to the disadvantage of the former. It pro- 

 duced greater activity in the carnivora, and greater fleetness in 

 the herbivora ; and so these have survived, and the ancient un- 

 wieldy ones have perished. 



Some naturalists seem to think that, as animals became more 

 active, they lost their plate-armour by natural selection, the more 

 active killing out the less active armour-plated animals. But I 

 think that just the reverse may have occurred. Animals became 

 active because they began to acq-uire rachitic skins, owing to a 

 lime-famine, this material having been used up mainly in making 

 rocks ! The deficiency of lime in the exo-skeleton may have not 

 only brought about more activity in the animal, but deficiency 

 of the same material in the endo-skeleton may have also brought 

 about smaller animals ; so that the two deficiencies may have 

 gradually contributed to create a much more active race of animals 

 than there had been before. 



It is not difficult to imagine that, although in some instances 

 the huge dish-cover carapace of an animal like the Glyptodon 



O 



