"THE SURVIVAL OF "THE FU'rES'T 109 



brethren far up the streams into the pools and marshes. 



Here the air dissolved in the water is foul ; they use the gills 

 less and the air-bladder or lung more. In the water, filled with 

 roots and stems of weeds, the paddle-like fins become jointed 

 and are used partly as legs. Finally during the recurring pe- 

 riods of drought, they will crawl out on land, somewhat like 

 the salamanders of to-day. 



Which will survive and make the next great upward step? 

 The cuttlefish is still hearty and vigorous, but has made 

 little, if any progress. The insect has improved on the crab. 

 The future evidently belongs to the vertebrates, descended 

 from the distanced and defeated primitive chordate. The 

 ganoid is promising, the shark is a conspicuous and marvellous 

 engine of speed and destruction. A salamander, driven out 

 on land, crawling among great club-mosses and weeds is not an 

 inspiring spectacle. 



We come down to early Mesozoic time. The eastern por- 

 tions of North America are now well above tide-water, but long 

 bays extend far into the land. Back from the shore, marsh 

 and dry upland alternate. Sharks and ganoids still persist 

 as well as cephalopods. But the amphibian has descendants 

 with whom these could never compete. Reptiles are every- 

 where prominent and dominant. They swim in the seas and 

 appear to be exterminating the surface-seeking ganoids. On 

 the land they run on four legs or stride on two. They own 

 the rich jungles and rivers with their banks or broad valleys 

 and bordering uplands. Some of them fly with bat-Hke wings. 

 Others are of huge bulk defended by coats of mail. Life is 

 easy and food abundant. Our present reptiles give but a 

 poor conception of the size and power, swiftness and strength 

 of these ancient forms. Birds are flying through the air, 

 though, perhaps, still somewhat reptilian in appearance. We 

 see a few small, scaly mammals, not one of them a match for 

 the reptiles. 



Once more which is the fittest? Later forms have not yet 

 arrived to give us the answer to our riddle. The reptiles 

 offer a great variety of conspicuous forms, some one of which 



