Turning to the Amphibia, the descendants of that stock which must be regarded as the ancestors of the Reptiles, the version of the sexual rôle which is adopted in these pages, that “Sexual Selection” in the older, Darwinian sense, does not exist, finds further support.
Among the tailless Batrachians—the Frogs and their kind—there is no “display” immediately preceding the act of pairing. The males seize upon the females and hold them in a close embrace which lasts for a very prolonged period, covering many days or even weeks, until the extrusion of the eggs, which he impregnates by successive emissions of the fertilizing element. What controls the orgasm no one has yet succeeded in discovering, but this is an important point, for it is essential that the seminal fluid should not be emitted until the moment the eggs are set free. The pairing act is here purely instinctive, as is shown by the fact that if a Frog in embrace be removed and replaced on some inanimate body, this will be treated as though it were a female.
With the tailed Batrachians—the Newts and Salamanders—the male commonly executes a very animated display which is followed by behaviour of a quite remarkable character. The display, which is always associated with vivid coloration, or the development of fin-like frills along the back, takes the form of amorous writhings and other gesticulations. At times he will hit his mate with his snout, and at others he will simply rub sides with her, as if to entice her to respond to his advances. These evolutions may be followed by an amplexus, an embrace. In some species, however, these performances are followed by behaviour which leaves one gasping with astonishment.
To begin with, there is no act of pairing, no coitus, but the male discharges a number of conical or bell-shaped “spermatophores,” each of which is crowned by a bunch of spermatozoa, the male germs necessary to ensure fertilization of the ova. These spermatophores adhere to the bottom of the stream, and are gathered up by the female, either directly, by placing herself in such a position that they can be seized by the lips of the genital opening, or by seizing the spermatophore, with its fertilizing germs, between her hind legs and pressing it home! The more one contemplates this extraordinary proceeding the more one marvels at the evolution of a departure from the normal sexual relations so inconceivably strange. Here one sees the purpose of the aphrodisiac in its true light. But for these facts it would have seemed certain that its primary object was to enable the male to relieve desire and at the same time to accomplish its end—the fertilization of ova—without undue waste. And this, in all the cases so far discussed, is possible only when the female has become inflamed with a like desire for coitus. But here the male finds relief, without more ado, by depositing the precious germs upon the ground. The display then is indeed to serve as an aphrodisiac. For the continuation of the race now rests entirely on the female. Any defect in the orderly working of her sexual appetite means the waste of the spermatozoa and the failure to effect fertilization. We cannot suppose that there is any realization of these facts, or any deliberate action on her part, but rather that she derives pleasurable feelings from the necessary passage of the spermatophore, which, probably, she recognizes by its smell.
The statement that the Frogs and their kind dispense with a display requires some qualification. For in the first place they, like their tailed relatives the Newts, develop secondary sexual characters, but these are of a quite peculiar kind. Among the Newt tribe, as has been mentioned, these characters take the form of frills and crests and vivid colours. They are intended to stimulate through the sense of sight, and arouse emotion, as a city is beflagged to welcome those it may delight to honour. The Frog tribe appeal to the musical sense, even though that music be of a barbaric kind. But, it would seem, when once the errant females have been drawn to the spot chosen by the males, no further aphrodisiac is used, the male simply seizing upon the female nearest at hand and, having once embraced her, she is not released again until the eggs have been extruded and fertilized. To maintain his hold, the forearm is often excessively muscular, while one or more of the fingers may be armed with pads. In some cases, as with the Himalayan Rana liebigi, the inner side of the arm and each side of the breast are studded with small conical spines. But the absence of ornament in these cases, as with such of the Newts where there is no amorous display before embrace, is significant.
And now, as touching the musical performances of these troubadours. These commence in the early spring. With many species, as with our Common Frog (Rana temporaria) nothing more than loud croakings are attained. But with others this “music” is enormously increased in volume by resonators in the form of air-sacs or wind-bags. We may surely, with some show of certainty, liken this “music” to the song of birds, and assign its primary purpose to the same cause—a device to advertise their presence to wandering females seeking mates. That birds sing after mates have been found, and later, is no doubt due to a general feeling of “fitness,” which finds expression in what has become the usual mode for such emotional states. Most people must have heard the spring concerts of our Common Frog; but these are incomparably surpassed in volume by the Edible Frog and the Bull Frog, which are provided with large, globular, inflatable, air-sacs in the throat, serving as voice-resonators. Such performances, however, are mere bawlings compared with some other species, which mew like cats, or bark like dogs. The most famous of all is the Brazilian “Ferreiro” or “Smith” (Hylodes faber), whose voice is one of the most characteristic sounds to be heard in Tropical South America. “Fancy,” says Dr. Gadow, “the noise of a mallet, slowly and regularly beaten upon a copper plate, and you will have a pretty good idea of the concert given generally by several individuals at the same time and with slight variations of tone and intensity.” When seized, the performer utters a “loud and shrill, most startling cry, somewhat similar to that of a wounded cat.” Another, a Paraguayan species, Phryniaxus nigricans, at the breeding season, utters a call note which consists of two clear, musical “rings,” followed by a long descending “trill” like that of our British Greenfinch. But, it is to be noted, both sexes in this case perform.
The period of sexual activity with perhaps the majority of animals is intermittent and extends over but a short period annually; with others potency is continuous, at least with the males, though desire becomes clamant only when aroused by external stimuli. But whenever this condition be aroused it invariably finds expression in exaggerated movements or vocal demonstrativeness. It uses the normal channels of expression, in short, but intensifies them. Now this period of sexual activity represents the maximum of “fitness” in animals, and it is not surprising, therefore, to find that when the barometer of vitality stands high some approach to the maximum of activity is indicated. In many birds this is revealed in song, though the earlier stimulating cause is absent. Among the cold-blooded frogs the same obtains. In the Edible Frog (Rana esculenta), for example, the males, which “are great musicians,” remarks Dr. Gadow, “go on singing for sheer enjoyment not only during the pairing time, but throughout the months of June and July. Warm, moonlight nights are the favourite times for the concert, which takes place in the water, beginning at sunset and continuing till early dawn. A few individuals utter a single note, ‘gwarr-oo-arr’ or ‘coarx’ but these are only preliminaries. The precentor ... begins with a sharp-sounding ‘brekeke’ and this is the signal for all the others to chime in with the same note, varied with all sorts of other sounds, bass, tenor and alto, each performer filling its resounding vocal sacs to bursting size, and these bags then look as if they acted as floats. When there are several hundred of these sociable creatures the din is continuous, and may be heard more than a mile off.”
From what has been said of the Amphibia, and especially of the Newts, it would seem that, among the land vertebrates at any rate, the sexual instincts in this lowest or simplest form are satisfied with the discharge of the germinal products. Many, however, have advanced a stage further and reveal the rudiments of that instinctive care for offspring which develops to higher and higher grades as we ascend in the animal kingdom, till at last, in the human race, where the offspring is desired for its own sake, we ascend to the highest plane of all. The varied means of expression which these rudimentary instincts take in the Amphibia have already been discussed in “The Infancy of Animals,” which preceded this present volume, and hence no more need be said on this head in these pages.