into orders is a matter of much difficulty and dispute. They are collectively spoken of as the Carinate, from the keeled form of their breastbone.

Widely apart from them stands another group made up almost entirely of large birds, which agree not only in having no power of flight, but also in certain significant structural characters, amongst which may be mentioned the absence of a keel on the breast-bone.

This latter group is sometimes spoken of as the order Struthiones from the ostrich (Struthio), which is its typical form. Sometimes these keelless birds are called Ratitæ. Besides the ostrich, the rhea, cassowary, and emeu are included within the group; also the small and nocturnal Apteryx of New Zealand and those giants of featherdom, the huge species of dinornis, all also of New Zealand and all now extinct.

With this our list of birds might close, but for a bird which anciently existed in Europe so strangely different from all modern kinds, that it must certainly be here adverted to. This bird is the Archeopteryx, found in fossil in the Solenhofen States.

The class Aves, like the class Mammalia, consists of animals with hot blood, but all birds have feathers and a number of other peculiarities of structure, as will appear later.

The next class to be adverted to is the class which includes all reptiles properly so-called-the class Reptilia.

The reptiles which exist in the world to-day may be classed in four well-marked sets, each of which has the value of an "order"-(1) crocodiles, (2) lizards, (3) serpents, and (4) tortoises. The names of these creatures alone suffice to indicate the fact that the class of reptiles presents us with an extraordinary amount of diversity of form as compared with the class of birds with which, nevertheless, reptiles have, as we shall hereafter see, very close relations. Indeed, in the diversity of kinds which it contains, the class Reptilia at the least fully equals the class Mammalia, especially if the extinct kinds are taken into consideration. The number of species of reptiles, both living and extinct, much exceeds also the number of living and extinct mammals.

To begin once more with forms which are the least strange and unknown, we may start with the little elegant and harmless lizards of our heaths and commons, which will serve as types of the order to which they belong-the order Lacertilia. That order is an extremely numerous one, containing many families, differing much in form. Our English lizards are true lizards, belonging to the typical genus Lacerta and to the typical family Lacertida. The rather well-known large American lizard, Iguana, is the type of another and very extensive family (almost entirely confined to America), while a nearly-allied family (Agamide) is an Old World group. Amongst the curious forms found in the latter family may be mentioned the frilled and moloch lizards of Australia, and those little harmless lizards of India which go by the formidable name of "flying dragons". (Draco). They are the only existing aërial reptiles-not that they can

truly "fly" at all, but they are enabled to take prolonged jumps, and to sustain themselves to a considerable extent in the air by means of the extremely distensible skin of their flanks which, when extended, is supported by a peculiar solid framework hereafter to be described. Some of the largest lizards are called "monitors," and are common in Egypt; they belong to the family Monitoride.

In the warmest period of the year, certain lizards are found in the South of Europe, called geckos. They have a power of running, not only up walls, but across ceilings by means of a peculiar structure of their toes. They are types of a large family (Geckotidae) widely spread over the world.

Another large family (Scincidae) has also its type in the South of Europe in the skink (Scincus), which was formerly supposed to possess much medicinal value. This large family contains a number of species which exhibit a series of gradations in structure leading to forms which have the external aspect of serpents. One such form is the perfectly harmless slow-worm, or blind-worm, of our own country, which in spite of its scientific name, Anguis fragilis*, is a legless lizard, and no snake.

Other lizards of a very different kind forming the family Amphisbæidæ are also legless, with the single exception of the genus Chirotes, which has a pair of anterior limbs, but no posterior ones. The name of this family is derived from the similarity of appearance presented by both ends of the body, so that either end looks as if ready to take the lead as "head."

A family of lizards familiar by name to us all from our childhood is the family of chameleons (Chameleonida). There are many species of chameleons, but they are found in the Old World only; they are among the most exceptional and peculiar of all lizards, but there is one form which is yet more so.

This most exceptional of lizards is one found in New Zealand, and named Sphenodon. Its external aspect would not lead the ordinary observer at all to suspect that it is so remarkable a creature as its anatomy shows it really to be.

The order Crocodilia contains, of course, the true crocodiles which are found both in the Old and New Worlds. It contains besides the alligators (which are peculiar to America), as well as the long and slendersnouted gavials which are now found only in India and Australia. At one time the number of kinds of this order was very much greater than at present, and interesting structural modifications have taken place in it during the course of ages, as will be pointed out later.

On the whole, the order of crocodiles makes a much nearer approach to mammals and birds-especially (strange as it may seem) to birds, than is made by any other group of existing reptiles.

Reptiles, however, once existed have left their remains fossilized (in

*For an explanation of the zoological system of nomenclature which has been adopted since the time of Linnæus, see CONTEMPORARY REVIEW for May, page 262.

the rocks of what is termed the "secondary" or "mesozoic" period), which reptiles in the structure of their skeleton approach much more closely to birds, and especially to birds of the ostrich order, than crocodiles do. Amongst these reptiles may be mentioned the huge Iguanododon (type of the extinct order Dinosauria), which once roamed over the Weald of Kent, and has left its remains in the Isle of Wight and elsewhere. Such remains were collected by its discoverer, the late Dr. Mantell, and are now preserved in our British Museum.

The crocodilia and some of the lizards of our own day are aquatic, but none live constantly in the ocean, as do the cetacea amongst beasts. This was, however, by no means always the case. In the secondary period just adverted to, huge marine reptiles (Ichthyosauria and Plesiosauria) lorded it over the other then inhabitants of the deep, and presented some noteworthy resemblances to the whales and porpoises which have since succeeded them.

But other remains preserved in those same secondary rocks show us that in that period which has been so deservedly called "the age of reptiles," not only did many huge species of the class stalk over the land (either browsing on its foliage or preying on their fellows), and many others swarm in the then existing waters, but it shows us that the atmosphere also had its reptilian tenants. Flying reptiles which formed the now extinct order, Pterosauria, and which were some of small, some of very large size, as truly "flew" as do the bats of our own day fly, and by a very similar mechanism. Moreover, if the Dinosauria present, as they do present, very noteworthy and interesting resemblances to birds of the ostrich order, no less noteworthy and interesting are the resemblances presented by these flying reptiles to ordinary-i.e., to " carinate" -birds.

The orders of extinct reptiles just referred to are not the only ones which formerly existed and have now passed away. There were reptiles with peculiarities in their teeth such as to have caused their order to be named Amnodontia, and it is members of this extinct order that the lizard Sphenodon more or less resembles, and it is this resemblance which gives it that special interest before noted.

We may now return from these very various extinct forms to enumerate other kinds of reptiles which exist to-day. But before doing so the fact may be adverted to, that though amongst beasts many forms have become extinct, yet the proportion borne by the known extinct forms to the living kinds is much less than amongst reptiles, and that while it is the most highly-organized reptiles which have ceased to exist, the highest mammals which are in any way known to us are those which at present inhabit the earth's surface.

In passing from the orders of crocodiles and lizards to that of serpents -i.e., to the order Ophidia-we might select as first to be mentioned kinds which much resemble the legless lizards; but such kinds are not familiar ones in Europe.

The only serpents met with in England are but of three species-two harmless snakes and the common viper, which latter is the only really poisonous reptile in this country.

Of the harmless snakes, the ringed or collared snake (Tropidonotus) is much the commoner and more widely diffused. It ought to escape destruction on account of the ease with which it may be discriminated from the viper by means of the white collar-like mark which appears so conspicuously just behind its head.

Our viper is the type of a large and poisonous family, but by no means all poisonous snakes are vipers. The deadly cobras belong to a different group, having much more affinity with our own harmless snakes than with the vipers. The rattle-snakes again form a family (Crotalida) by themselves.

There are such things as true sea-serpents, and they are poisonous. They are not, however, allies of any "sea serpent," such as every now and again figures in startling paragraphs in our journals. The true seaserpents are snakes of small or moderate size, which have their tails flattened from side to side, and which inhabit the Indian Ocean. Of other serpents which are not poisonous, the family of boas and pythons (which kill by crushing) is tolerably familiar to all who have visited zoological collections. There are many beautiful and harmless snakes, such as the families of tree-snakes and whip-snakes, but the snakes which more or less resemble legless lizards are burrowing forms which have the habits and more or less the appearance of earth-worms, such as those which form the families of Uropeltide and Typhlopside.

The last existing reptilian order (Chelonia) includes, besides the land tortoises of very various dimensions, a variety of aquatic forms.

The best known of these in this country, is the marine family (Chelonida), to which the edible and tortoise-shell turtles belong. The best known family in the United States and in the Continent of Europe, is the Emyde, to which pertain the terrapins or ordinary river tortoises. Besides these, however, there is a very small family (Trionicide) of curious and exceptional forms, called mud-tortoises (Trionyx).

The creatures which have next to be glanced at are those familiar forms, the frogs, toads and efts, which, together with their allies, form another class, the class Batrachia. These animals were long confounded with reptiles but are really widely distinct from them. They are arranged in four orders, three of which have living representatives. The creatures of the first order (the order of tailless Batrachians or Anoura)-frogs and toads-exist over almost all the habitable globe; and though the number of their kinds is very great, yet they are all extremely alike in organization. Many kinds (of both frogs and toads) are found to live in trees, the ends of their fingers and toes being dilated to enable them to cling to the surfaces of leaves. The most exceptional species of the whole group are the two tongueless toads, the Pipa of South America and the

Daclytethra of Africa, the last-named kind being the lowest of all known animals provided with finger nails.

Closely related to the frogs and toads are the efts so common in our ponds. These familiar English forms are represented in other countries of the Northern Hemisphere by creatures, some of which (as we shall hereafter see) are of very great interest indeed. The whole group constitutes the second Batrachian order-the order Urodela.

One of the most noteworthy forms of the order is the eft Proteus, which inhabits the dark, subterranean caverns of Carniola and Istria. Allied to this is the Menobranchus of North America and the Axolotl of Mexico. Other forms of the order are the American eft-genera Spelerpes and Amblystoma, the Menopoma, and the gigantic Salamander (Cryptobranchus) of Japan and China, the eel-like Amphiuma—with its very long body and minute legs-and the two-legged Siren of the United States.

The third order of Batrachians is one which contains very few species, but these are very strange, for though allied to frogs they have the appearance of snakes, or rather perhaps of worms. With long and slender bodies (marked by many transverse wrinkles), devoid of every rudiment of limb, they remind us of the before-noticed Anguis, Typhlops, and Uropeltis amongst reptiles. The Batrachians in question (which belong to the genera Cæcilia and Siphonops) form the order Ophiomorpha.

The fourth order of Batrachians is one which has entirely passed away and become extinct. It is the order Labyrinthodonta, and the species which composed it were, some of them, of large size, with great heads like those of crocodiles. Others bore more or less

resemblance to enlarged Ophiomorpha.

Every one knows that frogs begin their existence in the water as tadpoles, which have the habits and mode of life of fishes. Thus, the class Batrachia naturally conducts us to the class Pisces, the class of true fishes. This class contains a prodigious variety of forms, and is far more rich in species than any other of the classes before enumerated-even that of birds.

The fishes most familiar to us-such as the perch, carp, mackerel, cod, herring, sole, turbot, salmon, pike, dory, and eel-all belong to one great order called Teleostei, and which is made up of what are called "bony" fishes, though there are some bony fishes which do not belong to it. To the same order also belong the Murona, the electric eel (Gymnotus), the flying fishes (Exocetus and Dactyloptera), the sucking fish (Remora), the pipe-fish and sea-horse (Hippocampus), the diodon, the ostracion, the file-fish (Balistes), the largest of all fresh-water fishes (Sudis gigas of South America), with a multitude of other forms.

Certain more or less singular Teleosteans are classed together in a subordinate group of "Siluroids" (of which fish the Silurus is a type), and which group includes, amongst others, the singular, cuirassed fish Callichthys.