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 sea-serpents 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 Uropeltidæ and Typhlopsidæ.
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 (Chelonidæ), 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 Emydæ, to which pertain the terrapins or ordinary river tortoises. Besides these, however, there is a very small family (Trionicidæ) 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 Murœna, 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.