THE LONG ROAD 
times there was a gigantic dragon-fly, measuring 
more than two feet in the expanse of wings. Still 
earlier, there were gigantic mollusks and sea scor- 
pions, a cephalopod larger than a man; then gigan- 
tic fishes and amphibians and reptiles, followed by 
enormous mammals. But the geologic record shows 
that these huge forms did not continue. The mol- 
lusks that last unchanged through millions of years 
are the clam and the oyster of our day. The huge 
mosses and tree-ferns are gone, and only their 
humbler types remain. Among men giants are 
short-lived. 
On the other hand, the steady increase in size of 
certain other species of animals during the later geo- 
logic ages is a curious and interesting fact. The first 
progenitors of the elephant that have been found 
show a small animal that steadily grew through the 
ages till the animal as we now find it is reached. 
Among the invertebrates this same progressive in- 
crease in size has been noted, a small shell in 
the Devonian becoming enormous in the |Triassic. 
Certain species of sharks of medium size in the 
lower Eocene continue to increase till they attain 
the astounding dimensions in the Miocene and Plio- 
cene of over one hundred feet long. A certain fish 
appearing in the Devonian as a small fish of seven 
centimetres in length, becomes in the Carboniferous 
era a creature twenty-seven centimetres in length. 
Among the mammals of Tertiary times this same 
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