CHARACTERS OF THE CLASSES OF VERTEBRATE ANIMALS. 15 



Batracliians and the thin-skinned Lizards in a degree much superior 

 to any of the scaly class of Fishes : but the integument in many of 

 the Reptilia is covered or studded with horny or bony scutes. 



The generation of Reptiles has certain analogies with that of Fishes. 

 It is still effected in some species, as the Frogs and Toads, without 

 intromission, and in the same species we perceive a simultaneous 

 development of very numerous ova ; but the Batrachia form the 

 exception instead of the rule. The intromittent organ which exists 

 in the great majority of the class is also double in most of these, as in 

 Serpents and many Lizards. There are in the Reptilia both viviparous 

 and oviparous species ; but the fcetus in the former has no attach- 

 ment to the womb, and the eggs in the latter are hatched by ex- 

 traneous warmth : the young, after exclusion, receive no parental 

 cai-e or tuition in any species of the class. 



In investigating the various strata of the Earth, which form, as it 

 were, the grave-yards of as many successive generations of species 

 and classes, we meet with the earliest remains of air-breathing 

 Vertebrate animals in the triassic or Permian series, subsequent to 

 the deposition of the coal*, and we consequently infer that the date of 

 their existence, in this planet, is much later than that of Fishes. 

 But the Reptilian class seems soon to have acquired a vast extension, 

 and to have flourished under a variety of forms, developed also to 

 an enormous bulk, with powers for the acquisition and assimilation 

 of both animal and vegetable substances, of which the present state 

 of the class can afford no adequate idea. The deposition of the 

 chalk-formation seems to have been the date of the decline of the 

 Reptilia, when they gave way to as varied and colossal forms of 

 animals of a higher type of organisation. Amongst the numerous 

 species, genera, and even orders of the Reptilia, which at that period 

 became extinct, was one in which the anterior members of the 

 animal were developed into wings : these veritable " Flying-Dragons," 

 the " Pterodactyles," as they are termed, seem to have perished when 

 true winged Birds made their appearance. 



The present is scarcely a suitable occasion for speculating, even if 

 time permitted, on the probable changes in the atmosphere of our 

 planet which accompanied those undoubted revolutions in its crust, 

 by the investigation of which we obtain the evidence of this suc- 

 cessive introduction of organic forms ; otherwise we might discuss 

 the reasonableness of the surmise that the atmosphere was unfit to be 

 breathed by lungs during that vast lapse of time when fishes reigned 

 supreme upon earth ; or we might enquire if the atmosphere of the 



* The less conclusive evidence of foot-prinfs would carry back the dateof the Sala- 

 mandroid Cheirotheria to tlie coal formation. — Lycll, in Sillimans Juunial, vol. ii. p. 25. 



