The next forms of life to be developed, from the Monorrhini, were the Selachii (Amphirrhini), or true fishes, of the shark family, with two nasal cavities, swim-bladder, two pairs of fins, and jaws. From these evolved the Ganoidei, and thence all osseous fishes; and Dipnoi (mud fish), or hybrid fishes and amphibians, with both gills and lungs. These little animals live during winter in water, when they breathe air dissolved in water through their gills; and during the summer in mud, when they breathe with their lungs. Both these are placed in the Devonian period, in which have been found fossil sharks, etc. The next forms are Sozobranchii, or amphibians with persistent gills, from which evolved Urodela, or amphibians with transitory gills, but persistent tails, and legs; allied to the salamander. These are placed in the Carboniferous period, in which have been found fossilised amphibians. We next get Protamnia, or hybrid salamanders and lizards (frogs and toads), with no gills or tails, but possessing an amnion and cloaca. These represent the parent forms of the three great higher branches of vertebrates—Reptilia, Aves (which evolved from reptiles), and Mammalia, and are placed in the Permian period, in which have been found fossilised amphibians and true reptiles. Monotremata (Promammalia) are the next forms developed in our pedigree, the parent forms of the class Mammalia; with cloaca, amnion, and marsupial bones; which are placed in the Triassic period; and from which evolved Marsupialia, mammals with amnion and marsupial bones, but no cloaca; allied to the kangaroo and opossum of to-day. This species we place in the Jurassic and Cretaceous periods. From Marsupialia developed the large kingdom of Placentalia, which lose the marsupial bones and cloaca, and acquire a placenta, and which we divide into three main branches, according to the particular placental formation. The first division we call Villiplacentalia (tufty placenta), from which evolved Edentata (sloth, ant-eaters, and tertiary monsters), Cetacea (marine placental mammals, such as whale, dolphin, porpoise, and sea-cow), and Ungulata (horse, cow, pig, rhinoceros, and hippopotamus). The second division we term Zenoplacentalia (ring-like placenta), the earliest forms of which were Carnaria, or flesh-eaters, from which came Carnivora, or land beasts of prey (cats, dogs, bears, etc.), and Pinnipedia, or marine beasts of prey (seal and walrus). The third division we name Discoplacentalia (discoid placenta); and here we find, as the first development, the Prosimiæ, or tailed lemurs, quadrupeds with claws, and having the appearance of hybrid cats and monkeys. All these are placed in the Eocene period, in which stratum geologists have found fossilised placentals.