The kidneys are usually more or less lobed and placed posteriorly in the body cavity, especially in the Lacertilia, an order in which the two glands are sometimes united at their hinder ends. In serpentiform genera, e. g. Anguis, the right gland is in advance of the left, an arrangement more marked in the Ophidia. The glands are also elongated, and in Ophidia the separation into a series of lobes one behind the other is often carried so far that the lobes become independent, and are connected only by their union with a common ureter. There is a cortical as distinct from a medullary region in the Crocodile. The two ureters open on the dorsal wall of the cloaca. Remains of the Wolffian body ('golden yellow body') and its duct are to be found in many Lacertilia and Ophidia: they have also been found in Chelonia. The testes and ovaries are bilaterally symmetrical glands, but in Lacertilia the right organ, especially the ovary, is rather larger than the left and is placed slightly in advance of it. The differences of size and in position are greater in Ophidia. In both Lacertilia and Ophidia the glands are placed anteriorly to the kidney. A continual formation of new ovisacs takes place during life. The oviducts have simple apertures: the right is generally longer than the left.

The convolutions vary from time to time and are more developed during the breeding season. The vasa deferentia open with the ureters. There are two distinct types of copula-tory organs. The Lacertilia and Ophidia have a pair of eversible sacs opening into the cloaca, and when in repose lying under the skin of the tail. The surface of these sacs is covered with spiny processes. Their homologues are to be found in the female. The Chelonia and Crocodilia have two fibrous cavernous bodies closely united into a penis but traversed by a furrow and situated on the dorsal wall of the cloaca. In the Chelonia and Crocodilia two peritoneal canals or extensions of the coelome enter the penis. They have been observed to open on papillae at the base of the glans in the Chelonia: by pores at the base of the penis (or clitoris) in the Alligator, but in the Crocodile the two papillae in the same position are imperforate (Bridge). These canals are possibly the homologues of the abdominal pores found in Elasmobranchii and other fish. Accessory glands appear to be generally absent.

Glands opening into the cloaca have been found in Geckoes (female) and in Lacerta. The albumen of the egg, and the more or less calcareous shell are secreted by the glands of the oviduct.

Most Reptilia are oviparous. Some are viviparous, e. g. Zootoca vivi-para, the Blindworm (Anguis fragilis), Seps, Chilian Iguanas, among Lizards: many Chilian snakes, the Viper (Pelias berus), among Ophidia. Other viperine snakes and even a Boa Constrictor have produced living young in confinement, but it is doubtful whether they do so under natural conditions. The female Python disposes herself in coils round her eggs and incubates them for a prolonged period. During this process the temperature has been observed to rise as high as 960 F. within the coils1.

Many Lizards possess the power of casting off and of reproducing portions of the tail. The Reptilia pass into a lethargic condition in winter, where the cold reaches a sufficient degree of intensity. The aquatic Reptilia do the same in the dry season of hot countries.

All living Reptilia belong to one of four orders. The majority are inhabitants of the warmer parts of the world.

I. Chelonia (Turtles And Tortoises)

Body compressed in shape; the jaws covered by a thickened epidermis and devoid of teeth; dermal skeleton well developed; its dorsal portion or carapace uniting with the neural spines and ribs of the dorsal vertebrae, which are therefore immoveably fixed; its ventral ox plastron covering the abdomen more or less completely. Head, neck, tail, and limbs often retractile within the protection of the dermal skeleton. A urinary bladder and solid grooved copulatory organ present. Marine, freshwater, and terrestrial; occur in fossil state from the Kimmeridge Clay onwards.

II. Lacertilia (Lizards, Blindworm, &C)

Body covered by scales; as a rule two pairs of limbs, but one or other, or sometimes both pairs lost; eyelids moveable, rarely soldered and transparent; tympanic cavity seldom absent; jaws united firmly at symphysis; shoulder-girdle present when fore-limb is aborted; cloacal aperture transverse; a urinary bladder and double copulatory organ. Terrestrial; one marine form, Otocephalus (Amblyrhynchus) cristatus, from the Galapagos Islands. Iguana and Lacerta have been found fossil in Tertiary European strata. There are several fossil groups; see Huxley, Anatomy of Vertebrated Animals, 1871.

III. Ophidia

Body covered with scales; in the majority a special series of ventral ambulatory scales. Fore-limb, with shoulder-girdle always absent; hind-limb and pelvis represented in a few. Body elongated; symphysis menti ligamentous and extensible; eyelids transparent and always united; no tympanic cavity; a transverse cloacal aperture and double copulatory organ. Terrestrial, freshwater, or marine; fossil only in Tertiary strata (London Clay, &c).

IV. Crocodilia

Body covered by scales and partially by scutes; a long swimming tail; teeth implanted in sockets in the praemaxillae, maxillae, and dentary bones; longitudinal cloacal aperture and solid grooved copulatory organ. Freshwater. The largest living Reptilia. The Gavials are found in the Ganges, and the rivers of Borneo and N. Australia; the Crocodiles in Africa, India, and as far east as N. Australia, in Cuba and S. America; the Alligators are confined to S. America and southern part of N. America. All existing Crocodiles have procoelus vertebrae, and appear first in the Greensand; the extinct Teleosauria with amphicoelous or partly opisthocoelous (Steneosaurus) vertebrae come from the Lias, Kimmeridge Clay, Inferior and Bath Oolite. The genus Belodon is Triassic.

1 Martin-Saint-Ange states (p. 89, Etudes de l'Appareil reproducteur, Paris, 1854) that Geoffroy St. Hilaire and Florent Prévost succeeded in making the Common Grass Snake viviparous by-depriving it of water and maintaining a suitable surrounding temperature. On the Incubation of the Python, see Forbes, P. Z. S. 1881.