292 



SCIENCE. 



[N. S. Vol. VIII. No. 192. 



struggle for existence between those which 

 became inadapted and useless in the new 

 order of things went on more actively than 

 at present. The process of extinction of 

 the higher, more composite amphibians (the 

 labyrinthodonts) was largely completed by 

 the multitude of theromorphs and dinosaurs 

 which overcame the colossal Cheirotherium, 

 Mastodonsaurus and their allies.* 



During the centuries of the Trias the low- 

 lands became crowded, and the reptilian 

 life was forced in some cases to gain a liveli- 

 hood from the sea, for at this time was 

 ■eifected the change from small terrestrial 

 reptiles like Nothosaurus to the colossal 

 pleisosaurs and ichthyosaurs, in which digi- 

 tate limbs were converted into paddles, and 

 the ocean, before this time uninhabited by 

 animals larger than ammonites, cuttles and 

 sharks, began to swarm with colossal verte- 

 brates, the increased volume of their new 

 and untried habitat resulting in a tendency 

 to a corresponding increase in weight, just 

 as whales which possibly evolved from some 

 land carnivora in the early Tertiary waxed 

 great in bulk, the increase iu size, perhaps, 

 having been due to the great volume of their 

 habitat, the ocean. 



Nothing so well illustrates the advantage 

 to an incipient type as entering a previously 

 uninhabited topographical area, or a new 

 medium, such as the air. In the case of the 

 pterodactyles, the first vertebrates to solve 



*After ■writing the above lines I find the same view 

 expressed in Woodworth's Base-leveling and Organic 

 Evolution. He remarks : " The exact cause of their 

 decline is probably to be sought in the development 

 of the more powerful reptilia " (p. 225). Regarding 

 the circumstances favorable to reptilian life, he also 

 states : " In the development of the peneplain from 

 the high relief of the Permian and again at the close 

 of the Jura Trias the widening out of the lowland, 

 with plains and jungles, near tide-level, followed by 

 depression of the land, must have highly favored the 

 water-loving reptilia. It is to these geographical cir- 

 cumstances, I think, that we must look for our ex- 

 planation of the remarkable history of this class in 

 Mesozoic times " (p. 226). 



the problem of aerial flight, originating 

 and prospering in the early Mesozoic, they 

 held their own through the Cretaceous, 

 where at their decline they became, as in 

 Ornithostoma, colossal and toothless. "We 

 can imagine that the demise of this type 

 was assisted in two ways ; those with a 

 feebler flight succumbed to the agile, tree- 

 climbing dinosaurs ; while the avian tj^pe, 

 waxing stronger in numbers and power of 

 flight and exceeding in intelligence, ex- 

 hausted the food supply of volant insects, 

 and drove their clumsier reptilian cousins 

 to the wall, fairly starving them out, just as 

 at the present day the birds give the bats 

 scarcely a raison d'etre. 



3. THE PACIFIC COAST EEVOLUTIONS. 



It has long been known that there are a 

 greater number of insect faunae on the Pacific 

 coast and greater variation of species, with 

 more local varieties, than east of the Missis- 

 sippi river. It has also been shown by Gil- 

 bert and Evermann, as well as by Eigen- 

 mann, to apply to the fishes of the Columbia 

 and Frazer river basins. " Nowhere else in 

 North America," says the latter, " do we 

 find, within a limited region, such extensive 

 variations among fresh-water fishes as on 

 the Pacific slope." He also points out the 

 noteworthy fact that the fauna is new as 

 compared with the Atlantic slope fauna, 

 and ' has not yet reached a stage of stable 

 equilibrium.' As previously shown by Gil- 

 bert and Evermann, " each locality has a 

 variety which, in the aggregate, is diSerent 

 from the variety of every other locality;" 

 and he adds : ' ' The climatic, altitudinal 

 and geological differences in the different 

 streams, and even in the length of the 

 same streams, are very great on the Pacific 

 slope." 



It is evident that the variations are pri- 

 marily due to the broken nature of the 

 Pacific coast region, and to the isolation of 

 the animals in distinct basins more or less 



