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 live 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 rdle 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. Gunther, 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 
