The strength of the venom varies according to the species of Snake, and likewise the condition of the animal. The same species is more dangerous in hot than in cold or temperate regions. The bite is serious, according as the poison is more or less abundant in the glands, and probably with the degree of rage experienced by the animal, as Professor Owen supposes.
[Of Snakes in general it has been remarked that "all strangers in countries where these reptiles abound are apt to exaggerate their danger; but in a year or two they think as little of them as we do in England. I never knew an instance of a Snake attacking a person unless it was trodden upon or molested, and even then they almost always give warning by hissing, or endeavour to effect their escape. During my residence in the Cape colony, I have at different times trodden on them or kicked them in the grass unintentionally, but was never bitten."[20] This writer, however, could hardly have accidentally placed his foot upon a Puff-adder.[21]]
CHAPTER III.
The Order of Lizards.—Saurians.
This is the second order of the great section of Scaly Reptiles (Squamata), as distinguished from the Shielded Reptiles (Cataphracta). The name Saurian, Σαυρος, given by Aristotle to the genus of Lizards, has been more comprehensively applied to a group of Reptiles which have the body elongated, covered with scales, or having the skin rough like shagreen. They have, for the most part, four feet, the toes of which are furnished with hooked claws; their eyelids are movable, and their jaws armed with encased teeth; they have a distinct tympanum, a heart with two auricles and a single ventricle, sometimes partially valved, having sides and a sternum. They are not subject to metamorphosis, and, finally, they are furnished with a tail.
["By far the greater number of the Saurians," writes Dr. Günther, "are easily distinguished from the other orders of reptiles by their elongated form, by their movable thorax covered with skin, by the presence of legs, and by their general integuments, which are either folded into scales, or granular, or tubercular, or shielded; still, there are many Saurians which, at a superficial glance, might easily be taken for members of the preceding order—that of the Snakes; and it cannot be denied that there is a gradual transition from one of these orders to the other. On the part of the Saurians, we allude to those which have no externally visible limbs, and which combine with a greatly elongate, cylindrical body, the peculiar kind of locomotion we observe in Snakes. Yet the greater affinity of these reptiles to the ordinary Lizards is indicated by another character, which is in intimate connection with their mode of life. The Snakes, having movable maxillary bones, and mandibles not joined by a symphidis, are enabled to swallow other animals of apparently greater bulk than their own. In the Saurians the maxillæ are fixed and immovable, and the mandibles are joined by an osseous suture, so that the cleft of the mouth can be dilated only in the usual vertical direction. Moreover, in these limbless Saurians we always find bones of the shoulder hidden below the skin, whilst no trace of them can be discovered in the true Snakes. The motions of some Lizards are extremely slow, while those of others are executed, with very great, but not lasting, rapidity. Many of them have the power of changing their colours, which depends on the presence of several layers of cells loaded with different pigments; these layers the animal compresses by more or less inflating its lungs, whereby the changes in the coloration are effected."
Dr. Günther does not follow Dr. Gray in arranging all true reptiles into the two grand divisions of Shielded Reptiles (Cataphracta) and Scaly Reptiles (Squamata), but he includes the Crocodilidæ among the Saurians as a first grand division of them—Emydosauri, and the other Lizards constitute his second grand division of them—Lacertini. These latter are again primarily divisible according to the structure of the tongue. Thus, in the series of Leptoglossa, the tongue is elongate, forked, and exsertile, much as in the Ophidians; in that of Pachyglossa the tongue is short, thick, attached to the gullet, and is not exsertile; and in the Vermilingues it is Worm-like, club-shaped in front, and very exsertile.
The various genera of Saurians which have either not a trace of external limbs, or have them more or less diminutive and rudimentary—either the usual two pairs or one pair only, and in the latter case sometimes the fore and sometimes the hind pair being deficient—are included among the Leptoglossa, or the series which have a forked and protrusile tongue; and, so far as is practicable, we will commence by noticing the different serpentiform genera; only, in a classification which is not confessedly superficial, it will be found that the various Snake-like Saurians appertain to several distinct natural families, most of the other genera belonging to which have, in sundry cases, limbs that are well developed. Some of them, therefore, will have to be noticed as the different families to which they belong are successively treated of; and there will yet remain the curious serpentiform family of Amphisbænidæ, which Dr. Gray refers to his grand series of Shielded Reptiles (Cataphracta).
The same naturalist divides the Leptoglossa into two tribes, which he styles Geissosaura and Cyclosaura; and, as constituting particular division of the former, he includes under it the family Typhlopidæ, which Dr. Günther refers—as we have seen—to the order of Ophidians. In the series of Geissosaura, the scales of the belly and (almost always) of the back and sides are quincuncial, rounded, and imbricate; the tongue is narrow, short, flat, and but slightly forked; and the head is of a conical shape, and is covered with regular shields.
Of the families thus characterised, some only have distinct eyelids, as the families Acontiadæ, Ophiomoridæ, Sepsidæ, and Scincidæ; while others have the eyelids rudimentary and the eyes exposed, as the families Lialisidæ, Aprasiadæ, Pygopodidæ, and Gymnopthalmidæ. In the Acontiadæ the nostrils are placed in the enlarged rostral plate, with a longitudinal slit behind. The form of the body much resembles that of our common Orvet, or Blind-worm, and their limbs, when present, are so rudimentary that they can aid little in locomotion. One genus, Acontias, is without limbs, and the eyes are furnished with a lower lid, while the upper eyelid is rudimentary. Of this, one species, A. meleagris, inhabits South Africa; and another, A. Layardii, has been discovered in Ceylon. The genus Nessia has four rudimentary limbs, and the rostral shield is large, sub-conical, and depressed. In one species, N. monodactyla, the limbs are diminutive, the posterior placed far apart from the anterior, all being very short, weak, and undivided into toes. In another, N. Burtoni, each foot is divided into three minute toes. Both species are peculiar (so far as known) to Ceylon, and the habits of this family are much the same as those of our common Orvet (Anguis fragilis).