head, and for a peculiar substance called ambergris, found in masses in the intestines, and composed of a substance somewhat similar to cholesterine; this is used as a perfume. Dolphins (delphinidae).—This division comprises the dolphin, porpoise, and narwhal. They possess numerous conical teeth in both jaws, and the nostrils open by a single aperture at the top of the head. They inhabit most seas, and are very voracious. The narwhal is remarkable for the great development, in the male, of one of the incisors of the upper jaw. Sirenia. The Sirenia are also adapted for an aquatic mode of life, and comprise the Manatees and Dugongs, and are commonly called "sea cows." The snout is fleshy, and the nostrils are placed on its upper surface. The anterior limbs are turned into swimming paddles, and the hind limbs are entirely absent. There is a trace, however, of the pelvic arch; the intestinal canal is extremely long. The mammæ are pectoral, testes abdominal, and they have vesiculæ seminales. They are diphyodont, live on sea-weed, and keep near the shore. VIII. RODENTIA. This constitutes the largest order of Mammals. It has been calculated that nearly one-third of the known Mammals are Rodents, and of these rats and mice form one half. They possess two incisors in the upper jaw (sometimes four), but never more than two in the lower; the canines are absent, and there is always a wide interval between the incisors and molars; of the latter there are rarely more than four on either side of each jaw; the feet have usually five toes, each toe being furnished with claws. The distinguishing peculiarity of the Rodents (rodens, gnawing) is seen in the structure of the incisor teeth, which grow from permanent pulps; they are large, curved, and covered in front by a layer of hard enamel. The result of this is that the softer dentine wears away more rapidly than the enamel, hence the chiselled shape of the teeth. In some Rodents the collar bones are developed, in others they are absent; the testicles periodically descend from the abdomen into a temporary scrotum. To this order belong the hares, rabbits, beavers, squirrels, porcupines, guinea pigs, rats, mice, &c., &c. IX. INSECTIVORA.-These animals, so termed from the fact of their subsisting almost entirely on insects, comprise the moles, shrews, and hedgehogs. They are characterized by their peculiar dentition; they have incisors, canines, and molars, the last-named having their summits furnished with numerous cusps; clavicles are always present; the toes are furnished with claws, and the majority of the order have five toes to each foot, and are plantigrade. The mole has extremely small eyes, and is well adapted for a subterranean life. The hedgehog is covered with spines, and the muscles of the skin are greatly developed, so that the animal can roll itself up into a ball when threatened with danger. X. CHEIROPTERA (xelp, the hand; and TTEрóv, a wing), or bats, constitute a well-marked order of Mammals, and have the following distinguishing characteristics:-The fore limbs are much longer than the hind ones, and all the fingers, except the thumb, are greatly elongated, to support a membrane called the patagium, which is stretched between the fingers, and passes thence to the hind limbs (being attached to the sides of the body), and often includes the tail. This membrane is used in flight, and is analogous to the wing of a bird. When at rest, they suspend themselves by means of the thumb, which is furnished with a claw; from at least three of the other fingers claws are always absent; the clavicles are well developed, and the sternum is keeled for the attachment of the pectoral muscles; the feet are fivetoed, and unguiculate. Animals of this order have the three kinds of teeth, and the canines are well developed. They have no air cavities in the bones; the testes are retained in the abdomen, and only descend during the breeding season. They have large ears, small eyes, and are crepuscular or nocturnal in their habits. The most of them hybernate. They are divided into a. Insectivorous, e.g., all British Bats. XI. Edentata (Bruta) are the lowest order of placental Mammals, and comprise the ant-eaters, armadilloes, and sloths. They are characterized by the total absence of central incisors; the lateral incisors and canines are generally wanting, and sometimes the molars. The teeth, when present, are never covered with enamel, or replaced by a second set. The ribs exceed in number (twenty-three pair) that of any other Mammals; the toes are provided with strong, curved claws; the testes are abdominal. This order is divided into 66 a. Herbivorous and Arboreal, e.g., Sloths. b. Carnivorous and Terrestrial, e.g., Ant-eaters and Armadilloes. XII. MARSUPIALIA (Didelphia).—This order has received its name in consequence of its female members possessing a 'marsupium," or pouch, in which the young animal, which is always born in a very imperfect condition, is placed. This pouch is formed by a folding of the integument of the abdomen, and supported by the so-called marsupial bones; into the marsupium project long nipples from the mammary glands, through which the milk is forced by means of special muscles, as the young marsupial, when first born, is unable to suck. The oviducts open into vaginal tubes, which, in turn, open into a urino-genital canal, but there is no "cloaca." The scrotum is placed in front of the penis in the male, and is supposed by Professor Owen to be the marsupium turned inside out. The order is divided into— a. Herbivorous-Kangaroos, Kangaroo-Bears, Wombats, and Phalangers. b. Carnivorous-Native Devil, Native Tiger, and Bandi coots. XIII. MONOTREMATA (ornitho-delphia).—These animals form the connecting link between Mammals and birds, possessing some of the peculiar characteristics of each class. They possess a coracoid bone, which passes from the scapula to the sternum; the sternum is keeled like that of birds. A common cloaca receives the openings of the urino-genital organs and digestive canal; there are marsupial bones, but no marsupium; the mammary glands have no nipples; and the external ears are absent. There are only two known animals belonging to this order. a. Duck Mole (ornithorhyncus paradoxus), not unlike a small otter. It is covered with a short brown fur, and has a broad flat tail. The jaws are covered with horn, so as to resemble the beak of a duck (õpvis, a bird; and þúyxos, a beak), and are furnished with small horny plates, which serve the purpose of teeth. The legs are each furnished with five toes, which are webbed. b. Porcupine Ant-eater (echidna) is like a hedgehog, with a long snout, and is covered with hairs and spines. It is edentulous, and has a long flexible tongue. The feet have each five toes, which possess strong claws, but are never webbed. CHAPTER IV. AVES: GENERAL CHARACTERS. THE second great division of the Vertebrata consists of birds, and is thus defined by Professor Owen:—“Oviparous vertebrates, with warm blood, a double circulation, and a covering of feathers." The following are the more striking peculiarities observed in this division:-The skull articulates with the spine by a single condyle; the lower jaw articulates with the "os quadratum," which, in turn, articulates with the skull. There are no teeth, and the anterior limbs are changed into wings. The lungs communicate with air sacs scattered through the body, and many of the bones are pneumatic. The heart consists of four chambers, and the blood corpuscles are nucleated. OSTEOLOGY.-The skeleton of a bird possesses many points of interest, in consequence of its adaptation to the purposes of flight; it is compact and light; its compactness is owing to the great quantity of phosphate of lime which enters into its formation, and enables it to sustain the contraction of vigorous muscles; and the lightness is due to the existence of air cells, instead of marrow, which are indispensable for the purpose of flight. The cranial bones are anchylosed early, and the separate bones can only be demonstrated in the young bird; the lower jaw, however, remains distinct and movable. On examining a thin transverse section of one of the long bones of a bird under the microscope, it will be observed that the plasmatic canals exhibit oval dilatations. The cervical vertebræ vary in number, from nine in the sparrow to twenty-three in the swallow and swan; they |