8 REPTILES. 



large dimensions. The third numerical position in the fauna of the present day 

 is held by the crocodiles, of which there are some twenty-four species, all of 

 relatively large size, and all more or less aquatic in their habits. The fourth 

 existing order is now represented only by the lizard-like New Zealand tuateras, of 

 which there is probably but a single species ; although in past times there were 

 a host of allied forms. Of the five extinct orders the whole, or nearly the whole, 

 of their representatives ceased to exist with the close of the Secondary period, 

 that is to say, soon after the deposition of the chalk, and previous to that of the 

 overlying London clay. During that long period, or " world of reptiles," the class 

 attained a development which it never equalled before or since. The Dinosaurs, 

 which were by far the largest of all land animals, then filled the place now 

 occupied by Mammals ; the flying dragons played the role of the bats and birds of 

 the present day ; while the marine Plesiosaurs and fish-lizards did duty for whales 

 and porpoises. Of the mammal-like Reptiles, it will suffice to speak in the sequel. 

 With regard to the past distribution of the four existing orders, it may be 

 mentioned that the lizards and snakes, with the exception of two extinct suborders, 

 are practically unknown before the commencement of the Tertiary period that is 

 to say, until after the deposition of the Chalk ; hence they may be regarded as 

 essentially the Reptiles of the present day, when they attain their maximum 

 development. The tortoises and turtles, although a much more ancient group, 

 having existed throughout the Secondary period, are, however, still at or about 

 their zenith. The case is, however, very different with the ^crocodiles, which were 

 represented during the Secondary period by a host of forms quite unlike those of 

 the present day, and probably more numerous in species than their existing 

 representatives. Many of the extinct crocodiles also exceeded any of the living 

 forms in point of size. Still more markedly is this diminution noticeable in the 

 case of the tuateras, in which a solitary survivor represents a once abundant 

 group. 



Owing to the exigencies of space, our remarks on the present distribution of 

 the class must necessarily be brief. In the first place, it may be observed that 

 while no existing Reptiles are denizens of the air, only the turtles and sea-snakes 

 are habitual inhabitants of the ocean. Of the terrestrial and fresh- water forms, it 

 has been found that the distribution does not coincide very closely with that of 

 Mammals and Birds, so that the zoological regions into which the globe has been 

 mapped out from the geographical distribution of the latter scarcely hold good 

 for Reptiles. This discrepancy may, no doubt, be partly explained by the very 

 early period at which certain groups of the class, such as crocodiles and tortoises, 

 spread themselves over the surface of the globe. As regards the dispersive powers 

 of Reptiles in general, these, according to Dr. Giinther, are but limited. All these 

 creatures, he writes, " are much specialised in their mode of life and propagation, 

 and ill-adapted to accommodate themselves to a change of external conditions. 

 As air-breathing, cold-blooded animals they are unable to withstand prolonged 

 cold; they are therefore entirely absent in the Arctic and Antarctic zones; and 

 such as escape the effects of the winter months in temperate zones by passing 

 them in a torpid condition in well-sheltered places are not peculiarly 

 organised forms, but offshoots from those inhabiting warmer climes. The tropical 



