September 2, 1898.] 



SCmNGE. 



291 



extremities converted into pinions and the 

 hinder ones retaining the raptorial reptil- 

 ian form better adapted for aerial life. They 

 eked out a by no means precarious exist- 

 ence on flying insects and seeds, as well as 

 on the life in the soil or by the seaside, and 

 rapidly replaced certain older reptilian 

 types. The class of birds has become 

 about four times as numerous as the rep- 

 tiles, and outnumbers the mammals nearly 

 six times. 



We may now review the zoological 

 changes which took place at the time in- 

 cluding the end of the Paleozoic and the 

 opening of the Mesozoic. There was an 

 extinction of the Tetracoralla and their re- 

 placement by corals with septa arranged in 

 sixes ; an extinction of cystidian and blas- 

 toid crinoids, the dying out of old-fashioned 

 crinoids and echinoids (Palseocrinoidea and 

 Palseechinoidea) , followed by the rise of 

 their more modern specialized successors. 

 As rapidly as the brachiopods became di- 

 minished in numbers their place at the 

 sea-bottom was taken by the more active 

 and in some cases predatory bivalve and 

 univalve molluscs. As the trilobites be- 

 came extinct their place in part was filled 

 by their probable descendants, the Limuli, 

 which had already begun to appear, the 

 earliest types being Neolimulus, Exapi- 

 nurus and other forms of the Silurian, and 

 Protolimulus of the Devonian. The Lim- 

 uli of the Carboniferous, some with short 

 (Prestwichia and Euproops) and others 

 with long tail-spines ( Belinurus ) , suggest 

 long possession of the soil and consequent 

 variation and differentiation. 



The Eurypterida shared the fate of the 

 trilobites, and while there was a thorough 

 weeding out of the more typical ganoids, 

 leaving an impoverished assemblage to live 

 on through after ages, that singular primi- 

 tive vertebrate group, the Ostracodermi, 

 was wholly obliterated. 



On the other hand, with the incoming of 



a new order of vegetation, a great out- 

 growth of winged iasects, the represent- 

 atives of the orders of Lepidoptera and 

 Hymenoptera, now so numerous in species, 

 began their existence. 



By the close of the Appalachian revo- 

 lution probably all the orders of insects had 

 originated, unless we except the most modi- 

 fied of all, the Diptera, whose remains have 

 not been detected below the Lias. "With 

 but little doubt, however, the eight orders 

 of holometabolous insects diverged in the 

 Permian, if not near the close of the Car- 

 boniferous, from some protoneuropter ; the 

 progress in the differentiation of genera and 

 families becoming rapid either during the 

 Jurassic or directly after the lower Cre- 

 taceous, or as soon as grasses and deciduous 

 trees became in any way abundant. 



Very soon, too, after the close of the revo- 

 lution the ancestral birds and mammals 

 diverged from the reptiles, and of the latter 

 the turtles, plesiosaurs, ichthyosaurs, croco- 

 diles and dinosaurians, and soon after the 

 pterodactyles, came into existence. 



As a result of this revolution the mol- 

 luscan type was profoundly aifected, as at 

 the opening of the Triassic siphoniate Pe- 

 lecypoda, opisthobranchiate Gastropoda 

 and cuttles or belemnites appeared. "While 

 a few Orthoceratites lingered on after the 

 revolution, the Ammonites blossomed out 

 in an astonishing variety of specific and 

 generic forms. 



In summing up the grand results of the 

 Appalachian revolution and of the times 

 immediately succeeding, we should not 

 lose sight of the fact that the changes 

 in the earth's population were due no 

 less to biological than geological and to- 

 pographical factors. This process of ex- 

 tinction was favored and hastened by 

 the incoming of more specialized forms, 

 many of them being carnivorous and de- 

 structive, as, for example, nearly all fishes 

 and reptiles live on other animals. The 



