The Skull 105 
ads of creatures were changing in form and structure, 
some growing too bulky and helpless and vanishing, 
others developing powers of running, burrowing, flying 
and leaping. But it is a very remarkable and wonder- 
ful thing and very fortunate for us poor mortals, striving 
after knowledge of the past, that in each general class 
of creatures, certain ones should have found a niche 
where they were removed from the fierce struggle for 
Fic. 81.—Skull of young Alligator. Bones massive and solid, adapting their 
owner to an active aquatic life but to sluggish terrestrial movements; eye- 
cavities and brain-case very small, the jaws (organs of prehension) composing 
by far the major part of the head. 
existence, and where for year after year, century upon 
century, they and their descendants changed but little. 
We might mention Amphioxus and sharks among fishes, 
Necturus among amphibians, Sphenodon among reptiles, 
and the duck-billed mammal and others among _hair- 
covered creatures. These may be meaningless names, but 
if one will read about them and then examine their skins 
and skeletons in our museums, many a glance will be 
given into the ages of the past, compared to which the 
