The Courtship of the Crocodile—Amorous Lizards—Horned Cham?leons—A flagellating Terrapin—The Frog that would a-wooing go—Semo musical Frogs—Some marvellous instincts in Newts. The measure of the vitality of animals may be estimated by their response to stimuli; and their behaviour increases in variety and complexity as the nervous system develops. Our interpretation of that behaviour commonly leaves out of account the character of this responsiveness: we are apt to see proof of intelligence in acts which should be read as instinctive. And instinct is to be regarded as a co-ordinated response to stimulus, independent of prior experience.
The complexity of this response stands in very close relation to the structural complexity of the organism in which it occurs, and this because an ever-increasing number of mechanisms and actions must be set in motion to carry out the fulfilment of any given stimulus, as this is traced from the lower to the higher groups of animals: till at last we have to distinguish between movements that are merely reflexes, and those which are “instinctive.” The latter must be fulfilled by the former—the reflex 162actions are the agents of the instinctive. Indifferent performance in either, endangers the existence of the individual, and in some directions of the race itself.
The sexual instincts, with which alone these pages are concerned, are primarily stimulated and sustained by internal forces, generated, as we have already seen, by the juices of certain glands whose relation to the reproductive system has only recently been discovered. Though not commonly realized, and though denied by some, the sexual instincts are the dominant factors in the animal world. Even Man himself, the lord of Creation, knowing good and evil, cannot escape their overmastering rule. Commonly he is by no means inclined to rebel against this control But there be some who, in their arrogance, imagine that its overthrow is an end to be desired. Having scaled some slight intellectual eminence they fondly imagine this feat was accomplished by virtue of some spiritual grace of their own cultivation, and call to their fellow-men to emulate their example. But such preceptors are labouring under a strange delusion: they are suffering from a disease they wot not of, a “Disharmony,” as Metschnikoff calls it, a disease which blinds their perception of the motive power which has given them all that they believe themselves to have created. For these same despised instincts are the sacred fires of our being, and when they are quenched all that makes us human, love, ambition, and life itself will be extinguished. If the continuance of the race be a thing to be desired it is well that the choice should not be left to us.
Truisms are sometimes trite, and while it is a truism to say that no race can continue which does not reproduce its kind, it is more exact to say that, other things being 163equal, the race depends for its existence, primarily, on the efficient working of the sexual instincts. In the higher animals, the phenomena which these present are so complex that they often assume something more than a semblance of intelligent, purposeful behaviour. It is therefore necessary, for their right understanding, that they should be analysed in animals lower and lower in the scale of life till at last we come to the very simplest types of organisms wherein instinct can be said to play a part.
The lower we descend in the scale of animal life in our survey of behaviour during the reproductive period, the more the evidence seems to grow in favour of the interpretation of the Sexual selection theory adopted in these pages—the view that neither the formal displays nor the exaggerations of colour and ornament which so commonly accompany them, are due to female choice; a choice not necessarily conscious, but rather to be interpreted as the final abandonment to the finest performer of a number of suitors. On the contrary, this ornamentation, of whatever kind, is the expression of an intensification of the gland secretions which is manifested by the process of pigment concentration and a consequent intensification of coloration. Hand in hand with these developments it would appear goes an exaggeration of the normal movements which characterize the species when under the influence of great excitement, whether of fear or pleasure. At any rate, the displays of gaudily coloured and highly ornamental species are commonly more striking than those of sober hue.
On this rendering, the behaviour of Reptiles, Amphibia and Fishes, is much more readily interpreted, and this is even truer of the more lowly groups of animals such as Spiders, Butterflies and Beetles.
164Among the Reptiles, as among the birds and beasts, the desire to obtain territory seems to be strong. But the information to be gathered as to their behaviour in the search for mates, and after, is exceedingly small.
Sluggish by nature, all become animated under the stimulus of mate-hunger, and this is especially true of the males. As one would have expected, from what has just been said, desire is most demonstrative in brightly coloured and highly ornamented species. But even the dullest hued and most phlegmatic display quite surprising agility and animation under the fever of Love. Thus among the Crocodiles fierce battles are fought by rival males for the possession of some coveted female: and later the victor strives to dispel the apathy of his mate by caperings most undignified in a Crocodile. He will twist and turn, or rather twirl, round on the surface of his chosen pool, with head and tail raised high in air, and his capacious barrel of a body swollen out to bursting point. These antics are performed to the accompaniment of loud bellowings and roars heard at no other season of the year. But more than this, an appeal is made to the nose as well as to the eyes of his apathetic mate, for during all this parade of love he exudes from glands in the lower jaw, and tail, an almost overpowering smell of musk. At last, however, these antics have their reward, for sooner or later apathy awakens into interest, and interest ends in desire.
The Crocodile is colourless, or at least is monochromatic; not so many of the Lizards, which rival the birds in the vividness of their hues. With the birds the colours undergo no changes save such as are due to the incidence of light; with the Lizards, however, the bare 165skin is exposed and this can, as it were, be made to blush with all the colours of the rainbow. Having regard to what has been said already as to the sources of this coloration it is not surprising to note that here also the males are the more vividly coloured whenever the sexes differ in this particular. And further, it is among the most vividly coloured males that most animated displays take place when the endeavour is being made to excite the amorous instincts of the females.
The males of the genus Sitana are very brightly garnished. They possess a large throat pouch, coloured blue, black, and red when expanded, and this occurs only during moments of excitement, whether this is due to fear or pleasure. And at the same time the vividness of the coloration is greatly increased. No such secondary sexual characters are present in the female.
A variant on the throat pouch, of a much more striking character, is displayed by the Frilled Lizard (Chlamydosaurus kingi), wherein the tongue bones have become enormously elongated so as to project backwards on each side of the body almost as far as the base of the tail. With them they have carried a thin fold of skin, so that whenever the mouth is opened these bones stand out at right angles to the head and display a circular fold of skin stretched as it were on rods; or they may be compared to the ribs of an umbrella. The great Elizabethan frill thus formed, is displayed only during moments of great excitement, and the open mouth, at such times, is flushed with a vivid red, which, contrasting with the teeth, gives a very terrifying aspect to prospective enemies, and doubtless also proves a valuable asset as a “secondary sexual character.”
The display of a vividly coloured mouth during moments 166of sexual excitement, it may be remembered, occurs in some birds. Among reptiles it is a common feature. A good illustration of this is furnished by the Moustached Lizard (Phrynocephalus mystaceus), a native of Southern Russia. When violently excited it raises itself on its hind legs, curls and uncurls its tail, and opens its mouth to its widest extent, presenting, to our eyes, a quite fearsome aspect. This effect is immensely increased by the fact that the corners of the mouth are provided with flanges of skin, which at this time swell up into crescentic plates, the inner borders of which pass gradually into the rosy lining of the mouth, thereby causing it to appear much wider than it really is. So far this display has been witnessed only when the animal is under the influence of fear. But since we find that birds will make similar displays, both when under the stimulus of fear and that of sex, we may assume, with no little degree of certitude, that the same applies in the case of the reptiles, for the origin of the ornaments is almost certainly to be attributed to the same gland secretions which produce the secondary sexual characters of birds and beasts.
This, however, is no mere assumption, for we have some positive evidence as to the association of bright coloration with “courtship,” which has been furnished by Mr. Annandale, a naturalist of long experience and having a first-hand acquaintance with tropical life. He has given us a lively description of the courtship of the Malayan Lizard (Calotes emma). “The males,” he says, “are very pugnacious, and change colour as they fight. At the time of courtship a curious performance is gone through by the male, the female remaining concealed in the foliage hard by. He chooses some convenient station, such as a banana-leaf, or the top of a fence, and advances slowly towards the female. His colour is then pale 167yellowish flesh colour, with a conspicuous dark spot on each of the gular pouches, which are extended to their utmost. He stands upright, raising the fore-part of the body as high as possible, and nodding his head up and down. As he does so the mouth is rapidly opened and shut, but no sound is emitted. When he is driven away, caught, or killed, the dark spot disappears entirely from the neck.”
Plate 30.
 
Photo by W. Saville-Kent.
THE BEARDED LIZARD.
Paring moments of excitement the Bearded Lizard opens the mouth widely displaying a vividly coloured interior.
[Face page 166
Normally sluggish, the Lizards display, it will have been remarked, a quite surprising degree of animation when maddened by mate-hunger. Some exhibit a considerable degree of pugnacity. In Anolis carolinensis, for example, when two males meet they face one another, bob the head up and down two or three times, expand the throat pouch, lash their tails from side to side, and then, worked up to the requisite degree of fury, rush at one another, rolling over and over and holding firmly with the teeth. The conflict generally ends in one of the combatants losing his tail, which is eaten by the victor.
The Cham?leons include among their number species which have developed quite formidable horns, recalling those of the Rhinoceros or, better, of the extinct Arsinoetherium, since they are placed side by side instead of one behind the other. In Owen’s Cham?leon there are three such horns, two on the forehead and a median horn on the snout, and these are borne only by the males.
The marvellous play of colour which many Lizards display is commonly attributed indifferently to “protective coloration” and to “sexual se............