[11] In the British Museum Catalogue (1850) these Amphibians are styled _Batrachia Gradientia_, and are distributed under three families, comprising fifty-two recognised species. The class _Amphibia_ is divided by Dr. Gray into five orders--viz. _Batrachia_, _Pseudosauria_, _Pseudophidia_, _Pseudichthyes_, and _Meantia_. Of these the first, or the _Batrachia_, are divided into the sub-orders _Salientia_ and _Gradientia_, the latter consisting of three families, _Salamandridæ_, _Molgidæ_, and _Plethodontidæ_. The second order, _Pseudosauria_, comprises the families _Protonopsidæ_ (which contains the _Sieboldtia maxima_) and _Amphiumidæ_. The third order, _Pseudophidia_, consists of only one family, _Cæciliidæ_. The fourth order, _Pseudichthyes_, also contains one family only, the _Lepidosirenidæ_. The fifth order, _Meantia_, comprises the two families _Proteidæ_ and _Sirenidæ_. Twenty-four ascertained species are distributed amongst the last four of these orders; but the limits of this work do not permit of a more detailed notice of these various groups of _Batrachia Gradientia_. More recently, Dr. Günther, in his work on the reptiles of the Indian region, has pointed out certain structural characters connected with the generative system which show that the _Pseudophidia_ do not properly belong to the _Batrachia_; nor is their place in the system as yet quite satisfactorily determined. They seem rather to be a very humble form of reptile; while the _Pseudichthyes_ should rather be subordinated to the class _Pisces_: though, as we have seen, there are naturalists who would refer all of the _Batrachia_ to the fish class, certain forms amongst them rising to a parallelism of development with _Reptilia_, but still not constituting true reptiles. The mode of reproduction especially is in favour of this view. Both _Pseudophidia_ and _Pseudichthyes_ are intertropical or subtropical animals, whereas the rest of the _Batrachia Gradientia_ belong almost exclusively to the northern temperate zone; any exceptional case occurring probably in very elevated regions. Of sixty-six ascertained species, forty-nine are American, and there are five from Japan, inclusive of the _Sieboldtia maxima_. But more species have been discovered since the catalogue cited has been drawn up, and of course there must be many yet to be discovered. Five species are referred to the _Pseudophidia_, and three only to the _Pseudichthyes_.--ED. CHAPTER II. OPHIDIAN REPTILES, OR TRUE SNAKES. Reptiles are, as has been said in the preceding chapter, Vertebrated Animals, breathing by lungs, having red and cold blood; that is to say, not producing sufficient heat to render their temperature superior to that of the atmosphere. Destitute of hairs, of feathers, of mammary glands, and having bodies covered with scales.