Ch. XXV.] AIR-BREATHERS Ei THE COAL. 513 



In a second specimen of an erect stump of a hollow tree 15 inches 

 in diameter, the ribbed bark of which showed that it was a Sigillaria, 

 and which belonged to the same forest as the specimen examined by 

 us in 1852, Dr. Dawson obtained not only fifty specimens of Pupa 

 vetusta and nine skeletons of reptiles belonging to four species, but also 

 several examples of an articulated animal resembling the recent centi- 

 pede or gally-worm, a creature which feeds on decayed vegetable mat- 

 ter, see fig. 562. Under the microscope, the head, with the eyes, 

 mandible, and labrum are well seen. It is interesting, as being the 

 earliest known representative of the myriapods none of which had pre- 

 viously been met with in rocks older than the oolite or lithographic 

 slate of Germany. 



Rarity of Vertebrate and Invertebrate Air-breathers in Coal. 



Before the earliest date above mentioned (1844) it was common to 

 hear geologists insisting on the non-existence of vertebrate animals of 

 a higher grade than fishes in the Coal, or in any rocks older than the 

 Permian. Even now, it may be said that we have made very little 

 progress in obtaining a knowledge of the terrestrial fauna of the coal, 

 since the reptiles above enumerated seem to have been almost all 

 amphibious. Negative evidence should have its due weight in palse- 

 ontological reasonings and speculations, but Ave are as yet quite un- 

 able to appreciate its value. In the United States, about live millions 

 of tons of coal are annually extracted from the coal-measures, yet I am 

 acquainted with no fossil insect which has yet been met with in the 

 carboniferous rocks of North America. But as we have detected car- 

 boniferous insects in Europe (see p. 494), no one would now conclude 

 that at the period of the Coal this class of invertebrata was unrepre- 

 sented in the forests of the Western World. In like manner, no land- 

 shell, no Helix, Bulimus, Pupa, or Clausilia, nor any aquatic pulmonif- 

 erous mollusk, such as Limnea or Planorbis, is recorded to have come 

 from the coal of Europe, worked for centuries before America was dis- 

 covered, and now quarried on so enormous a scale. But no one 

 would now infer that land-shells had not been called into existence in 

 European latitudes until after the Carboniferous period. 



The theory of progressive development might account plausibly for 

 the absence of Chelonian and Saurian reptiles, or of Birds and Mam- 

 mals, from the Coal-Measures, because it may be supposed that at so 

 early a stage in the earth's history no organic beings higher than 

 sauroid batrachians had made their appearance. But this same theory 

 leaves the scarcity of the invertebrata, or even the entire absence of 

 many important sections of them, wholly unexplained. When we 

 generalize on this subject, we must not forget that, so lately as the 

 year 1851, we knew of only two or three individual land-shells and 

 some twenty specimens of insects, and scarcely double that number of 

 individual reptiles in carboniferous rocks, and some of these reptiles 

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