CHARACTERS OF REPTILES THE CHAPTER VIII Reptiles HE reptiles are the only vertebrates which are cold-blooded and which without exception breathe by lungs and never at any period of their lives breathe by gills, as do the fishes always and the amphibia for a portion of their lives. They have also invariably a scale-covered skin, in which also there may be supplementary bony structures, such as the bony part of the "box" of the tortoise, and the strong plates in the skin of crocodiles. They possess neither feathers nor hairs. The skull is fixed on to the succeeding vertebral column by one rounded joint or condyle as in birds, while the mammals and the amphibia have two of these, one on each side. It is from the amphibia that it is most difficult to divide reptiles, a fact which is embodied in the confusion of the two into one group, called "reptiles" by some of the older authors, and "amphibia" by some others. In past times, as is natural on any theory of evolution, the reptilia and the amphibia gradated into one another, and no very hard and fast line can be drawn. The living representatives of these groups can, however, be distinguished by the characters already enumerated. There are other anatomical characters into the consideration of which we shall not enter here. The most obvious character of the reptile is its complete covering of scales. Some extinct groups, such as the Ichthyo HATTERIA AND THE LIZARDS saurs, seem to have had smooth scaleless skins, but no living reptile is without this tesselated armature. The existing reptiles are to be divided into five orders, but their numbers to-day are much below their numbers in past times. The reptilia are clearly a waning race as a whole, though of the existing orders most are more numerous now than they ever have been so far as the geological evidence at our disposal enables as to say. As to their numbers to-day, Dr. Gadow asserts that there are about 3,500, so that there are more reptiles than mammals, but considerably fewer than there are fish and birds; for of the latter we know some 10,000, and of fishes some 8,000, while there are something like 2,700 mammals and about 1,000 amphibians. The enormous majority of living reptiles belong to the groups of lizards, snakes, and tortoises. There are but few crocodiles, and Hatteria is the only living example of its own group. LIZARDS: THE ORDER LACERTILIA The only other reptiles with which the lizards could be possibly confounded are the crocodiles, snakes, and the New Zealand Hatteria, which is the sole living representative of an otherwise extinct order, Rhynchocephalia. The turtles and tortoises are so distinct that there is no danger of confusion for the most ignorant of Natural History. From the crocodile tribe the lizards are to be distinguished by a variety of characters, which are, however, deep seated, and thus not easily appreciable to one examining the animals in a menagerie. As to purely external characters, it is most difficult to draw a line. In the crocodile tribe the nostrils are very plainly on the upper surface of the snout and protrude somewhat, which is of course in relation to the aquatic life of these creatures. The vent is a longitudinal orifice and not a transverse one as in HEART OF REPTILES lizards and snakes. The size is greater than that of any lizard; but it must be remembered that a large monitor lizard comes not far behind a smallish crocodile. Crocodiles are invariably aquatic, lizards are very rarely so. We must necessarily mention a few internal characters to emphasize the separation of lizards and crocodiles. In the latter the teeth are always confined to the upper and lower jaws; in lizards they stray on to the bones of the palate in many cases; furthermore each tooth of a crocodile is implanted in its own particular socket, while in lizards the teeth are attached side by side to the bones which bear them without lying at some distance apart and each like a peg in a hole in these bones. The heart of the crocodile is more completely four-chambered than is that of the lizard, in some of which, however, there is a tendency in the same direction. On the whole the lizard tribe is on a lower level of organization. Lizards are excessively numerous and occur in almost all parts of the world, except in very cold regions, such as the extreme north. They chiefly abound in the tropics.. The general aspect of a lizard is familiar to every one. But it is not so easy as it seems to differentiate a lizard from a snake. For among the lacertilia there is a distinct tendency to lose the limbs, an event which has occurred in many of the families into which the order is divisible, and thus produces a likeness to a snake which is after all superficial. Nevertheless, the two orders, the Lacertilia and the Ophidia, are very nearly akin. Some differences between them will be Idealt with later. THE HELODERM Lizard Of lurid coloration is the Arizona heloderm, or “gila monster as it is often termed in the United States, in the southernmost of which it lives. There would SPECIES OF HELODERMA 66 appear to be two distinct kinds of heloderma, viz. H. suspectum and H. horridum. One epithet is good, the other bad. It is truly "horrid" in the applied as well as in the literal sense of that adjective, for the skin is roughened with warty scales underlain by bony nodules. Suspectum" is too dubious an adjective; for this lizard is not merely suspected but known to be poisonous, being in fact the only lizard which has this qualification. It was thought some little time ago that the rare Lanthanonotus of Borneo was also poisonous; but recent study has proved that, while related to Heloderma, it lacks the grooved teeth of the latter. Experiments tried with Heloderma as the main actor with the subsidiary parts played by various frogs and guinea pigs has satisfied every one that this lizard does bite with a poisoned effect; moreover the salivary glands, or rather some of them, are furnished with several ducts which open in close apposition to the grooved teeth; along the grooves run the poison which is thus necessarily injected into the wound made by the teeth. In fact, the gila monster poisons precisely in the same fashion as the venomous colubrines, those non-viperine snakes which are poisonous. On the other hand, the courageous Dr. Shufeldt allowed himself to be bitten by one of these lizards, but experienced no serious inconvenience "beyond the ordinary symptoms that usually follow the bite of an enraged animal." Like most lizards this animal is lethargic and melancholy in appearance in captivity. It seems indeed to have fewer and shorter repetitions of those periods of briskness which even the most sedentary of lizards show at times. It can, however, be roused, and then its wrath is terrible. Under these circumstances, observes Dr. Shufeldt, "the animal quickly rears its body from the ground by straightening out its limbs, wheels about, opens its mouth widely, |