Grey-brown, smooth-bodied slow-worm angling through various grasses.Pl. 90.][K 144.Slow-worm.Anguis fragilis.View Larger Image Here.
Pl. 90.][K 144.Slow-worm.Anguis fragilis.
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Snake looped around itself in short grasses.Pl. 91A.]Grass Snake casts its skin.1. Immediately before sloughing.View Larger Image Here.
Pl. 91A.]Grass Snake casts its skin.1. Immediately before sloughing.
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Curled snake in center of surrounding cast skin.Pl. 91B.]Grass Snake casts its skin.2. Operation nearly complete.View Larger Image Here.
Pl. 91B.]Grass Snake casts its skin.2. Operation nearly complete.
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Coiled snake; small amount of cast skin showing underneath it.Pl. 91C.]Grass Snake casts its skin.3. In new attire.View Larger Image Here.
Pl. 91C.]Grass Snake casts its skin.3. In new attire.
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Close-up of head showing small overlapping scales.Pl. 92A.]Head of grass snake.A. Difference of form and scaling in heads of the two species.View Larger Image Here.
Pl. 92A.]Head of grass snake.A. Difference of form and scaling in heads of the two species.
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Flattened head with very small scales compared to body.Pl. 92B.]Viper.B. Difference of form and scaling in heads of the two species.View Larger Image Here.
Pl. 92B.]Viper.B. Difference of form and scaling in heads of the two species.
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Light brown snake with black vertical bars on sides, curled on tan, blue, and grey rocks.Pl. 93.][L 145.Grass Snake.Tropidonotus natrix.View Larger Image Here.
Pl. 93.][L 145.Grass Snake.Tropidonotus natrix.
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It was in the Slow-worm that the discovery was made in 1886 of vestiges of a degenerate median eye connected with the pineal gland—a discovery that set all the biological investigators of the world at work. The same gland has in the last few years been found to have important influence in controlling the growth of the body in all vertebrates.
The Slow-worm is generally distributed throughout the British Islands, with the exception of Ireland; it is much more plentiful in the south and south-west of England than in the east or north, but even in the south it is much more abundant in some districts than in others. Its wider range includes all but the extreme north of Europe, Western Asia, and Algeria.
Grass Snake(Tropidonotus natrix, Linn.).
Before entering upon a description of the greatly feared though harmless Grass, Ringed, or Common Snake, it would be well to say a few words on the structure of Snakes in general, and so avoid some amount of repetition, for in a general way our three species are alike.
The Slow-worm, our legless Lizard, affords a convenient transition to the Snakes; but the bony skeletons of Snake and Slow-worm exhibit considerable differences. No Snake possesses a breastbone, bladebone, or collarbone, so that all the ribs are free at their ends, and they are strongly curved to produce the cylindrical form of body. When bulky food is taken the ribs can be flattened out to allow of the necessary distension of the body until digestion and muscular pressure have reduced the bulk. The bones of the skull are connected so loosely that the head can be flattened and widened, so that the mouth can admit prey equal to three times the size of the Snake's head under normal conditions. To assist in the swallowing of such large bodies, the two halves of the lower jaw have no bony connection but are united instead by elastic ligaments, so that each half can be moved independently of the other, and by the alternate movement of the two sides with the teeth all pointing backwards the food is worked back to the throat. There are other teeth on the roof of the mouth which make it difficult for living prey to struggle forward and escape when once it has been seized. The teeth are all thinly coated with enamel, and are not planted in sockets. If they should get broken by the severe work imposed upon them, they are soon replaced by others which lie in reserve. Poison fangs are much larger than ordinary teeth, and the enamel is folded so as to produce a groove down which poison is pressed from a gland into the wound made by the point of the fang. The fang is hinged at its base and ordinarily lies pressed back upon theupper jaw, and is only "erected" when the Snake is prepared to strike.
Line drawing--special large symmetrical scales on the snake's head; also known as plates.The Head Shields of a Snake.r, rostral shield;ff, anterior and posterior frontal;v, interparietal;s, supraocular;o, parietal;nn', nasal;l, loreal;a, preocular;p, postocular;uu, upper labial;tt', temporal;m, mental; **, lower labial;cc, chin-shields.—After Günther.View Larger Image Here.
The Head Shields of a Snake.r, rostral shield;ff, anterior and posterior frontal;v, interparietal;s, supraocular;o, parietal;nn', nasal;l, loreal;a, preocular;p, postocular;uu, upper labial;tt', temporal;m, mental; **, lower labial;cc, chin-shields.—After Günther.
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Externally the Snake is covered by small overlapping scales on the upper parts and by broad plates on the under surface. The head is covered mainly by shields, each of which has adefinite name, but for the purposes of this book it is not necessary to enter upon a tedious recital of these terms, beyond giving them for reference under the diagram of a Snake's head.
Curled skeleton, enlongated head, hinged jaw, free-end ribs.Skeleton of Snake.View Larger Image Here.
Skeleton of Snake.
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The eyes of a Snake are always wide open, for there are no movable eyelids to close them. The eyeball has slight power of movement under its transparent cover, which protects it much as the watch-glass protects the delicate hands of the watch. As in the Slow-worm, there is no external indication of ears, though these are present under the scales. The very long and slender tongue divides forwards into two branches, and when not in use is drawn into a sheath at its base. It is constantly used to ascertain the nature of things by contact, and for this purpose is protruded through a little gap in the front of the upper jaw. The gape of the mouth extends far beyond the eye. The forward extremity (glottis) of the wind-pipe can be thrust outside the mouth when, owing to the passage of a bulky victim, there is danger of obstruction by compression.
The British Snakes represent the two families Colubridæ and Viperidæ.
Every summer and autumn our daily newspapers affordevidence that on the subject of Snakes the average man has not advanced in knowledge beyond that of his prototype a thousand years or so back. With all that has been done in various ways during the last half-century to spread knowledge of natural things, it is astonishing that editors should admit scare reports about Snakes without a line to set the reader right. Internal evidence shows that nine-tenths of these alarming reports about poisonous and aggressive Snakes refer to the innocuous Grass Snake. This is the kind of thing that reflects the vaunted intelligence and calmness of the average Briton:—
"An enormous snake was killed yesterday at ——, only a few yards from where some children were playing. The Rev. Mr. Blank courageously seized the reptile behind the head, but when it hissed savagely at him he was forced to throw it down. Its head was then smashed with a pole, and finally it was despatched with the aid of a spade. The venomous monster was found to be over three feet in length. Its nest was found and a large number of eggs destroyed."
Solid coloured female, subtle markings; male has bold zigzag line down middle of back, spots on sides.Pl. 94.][L 148.Vipers.The two sexes: the lower figure is the male.View Larger Image Here.
Pl. 94.][L 148.Vipers.The two sexes: the lower figure is the male.
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Grey-brown snake with dark cross-bars over the back and spots on sides; brown pebbles, grey rocks.Pl. 95][L 149.Smooth Snake.Coronella austriaca.View Larger Image Here.
Pl. 95][L 149.Smooth Snake.Coronella austriaca.
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A very elementary knowledge of our native snakes—such as all country folk might be expected to possess—would dispose of all this fear and sensation, for no one has ever found a Viper or Adder—our only venomous snake—that measured quite as much as three feet, or that had a nest of eggs.
The Grass Snake is our largest British species, full-grown females averaging four feet in length; the males a foot less. Exceptional examples are little short of six feet, and in Italy the same species attains to a length of eight feet. It is of graceful form, the body tapering gently from its middle to the very slender tip of the tail. The long, narrow head, covered with large shields, ends in a blunt snout, with eyes and nostrils at the sides. The rather large eyes have round pupils circled with gold and a dark brown iris. Just behind the head there are two patches of yellow or orange (sometimes white) forminga bright collar which serves to indicate this species at a glance. In large females this collar is sometimes missing. Immediately behind it are two patches of black, often united in the middle line, and behind these the ground colour of grey, olive, or brown is uniform to the tip of the tail. Upon the ground colour of the back are laid two rows of small blackish spots, and a row of short vertical bars along each side. The underside, which is covered with broad plates, is chequered in black and white (or grey); but is sometimes entirely black. The tail accounts for about one-fifth only of the total length.
Apart from the head-shields and the broad plates of the underside, the Grass Snake is covered with nineteen rows of small, overlapping, lance-shaped scales with a central ridge or "keel." These scales are an outgrowth from the skin, and when the Snake moults they do not fall off as the hairs of fur-clad animals do, but the entire skin with its scales is cast intact. It separates first at the edges of the jaws, and the Snake pushes against the ground, stones, or plant stems until the loose skin is behind the head. Then it glides out of the remainder, reversing it in the process. In these discarded sloughs the lens-like covering of the eye will be found unbroken.
In the autumn the Grass Snake retires to some safe shelter under the roots of trees, among the stubs of a coppice, under a brushwood pile or fernstack, in order to pass the winter in sleep. As a rule, several or many associate in hibernation, and when found they are usually twined together in intricate knots. Here they remain until March or April, when the Frogs, Toads, and Newts, emerging from a similar retirement, are available for a good meal. About this time the males seize the females in their jaws, and with their bodies entwined pairing takes place. Some time between June and August the female seeks some convenient mass of fermenting vegetable matter amidst which to burrow and deposit her eggs. If a heap of fresh stable manure is available she will prefer it, the heat hasteningincubation. The eggs—which may number a dozen or anything up to four dozen—are equal-ended ovals with a tough, parchment-like shell, and all connected in a string. As soon as laid they begin to absorb moisture from their surroundings, and increase in size until they are about an inch and a quarter in length. They hatch in from six to ten weeks, according to temperature, and the baby Grass Snakes measure from six to eight inches. Before hatching they are provided with a special egg-tooth projecting from the front of the jaws, which enables them to pierce the egg-shell. It soon becomes loose and drops off after its special function has been performed. The young Snake sheds its skin before taking its first meal, and thereafter goes through the same process four or five times in a year.
The Grass Snake appears to have a life comparatively long. The female is about four years old, with a length of two feet, before she begins to breed. Gadow mentions a fine female which he had alive for nine years, and during this period her length increased from thirty-five to forty-two inches.
Although the Grass Snake may be found frequently about ponds and ditches where there are Frogs, Toads, and Newts to be caught, it is by no means restricted to such resorts, but may be met with on chalk hills, sandy heaths, and other places far removed from water. In addition to the amphibians mentioned, it feeds occasionally on fish, mice, and small birds. The young Snake takes worms, tadpoles, and the young of newts, frogs, and toads. It swims well and often enters the water to obtain its prey. Although an agile reptile, it may be caught without difficulty where the ground is not too rich in mouse runs or too well covered with furze. The undulations by which it progresses are always horizontal, not vertical as sometimes represented by imaginative artists. When captured it seldom makes any attempt at biting, though it will hiss freely and snap its jaws. It usually seeks rather to disgust its captor by the voiding of a fetid secretion with a strong odour of garlicamong other objectionable scents. It soon becomes gentle and tame.
The Grass Snake is widely distributed over England, Wales, and the south-eastern parts of Scotland. It appears never to have reached Ireland. Various attempts have been made to introduce it in the latter country, but the prejudices of the people and their respect for the legendary miracle of their patron saint have always prevented the Snakes from establishing themselves.
Smooth Snake(Coronella austriaca, Lacepede).
Although in general appearance similar to the Grass Snake the Smooth Snake in the hand exhibits a sufficient number of differences to make its identification easy. The smoothness which gives it a name is at once evident to our sense of touch, and is due to the fact that all its scales lack the little keels or ridges that give a certain roughness to the common species. It never attains to so large a size as the Grass Snake, its maximum length being two feet.
The ground colour of this snake on the upper side is grey, brown, or reddish, with small black, brown, or red spots, which are usually in pairs; occasionally there are three lighter longitudinal stripes. The upper part of the head is sometimes blackish; this is more frequently so in young examples. A dark streak runs from the nostrils and through the eye to the angle of the mouth. This streak may be prolonged, even to the tail. On the underside the colouring is some tint of orange, red, brown, grey, or black, with or without black spots or dots. The eye has a round pupil like that of the Grass Snake, and this helps to give it a similar gentle appearance.
Prior to the year 1853 British specimens had been regarded as mere variations of the Grass Snake, but in that year it was captured by Mr. F. Bond at Ringwood by the New Forest, though it was not recorded under its proper name until sixyears later. It has been found since in other parts of Hampshire, in Dorset, Surrey, and Berkshire; in some places abundantly, especially those in which the Sand Lizard occurs, this being the Smooth Snake's favourite prey. Its usual resorts are heaths, stony wastes and wooded hillsides. Its food consists mainly of Lizards, but it also takes young Snakes and Slow-worms; occasionally it consumes mice and mice-like mammals including the Voles and Shrews. When these are sufficiently large it is said to coil around them in Boa-constrictor fashion.
Pairing takes place soon after emergence from hibernation in spring. As in the case of the Slow-worm and the Common Lizard, the eggs are retained until the young are ready to hatch out, and they are born about the end of August. They vary in number from two to fifteen, but usually there are about six to a birth. They are enveloped in a thin membrane which is ruptured immediately, and the Snakes are seen to be about five or six inches in length.
Like the Grass Snake this species emits an objectionable odour when captured, and at first attempts to bite, but this unfriendly phase passes quickly, and it becomes perfectly tame and exhibits a considerable amount of intelligence.
It may be as well to add that, if we count the rows of small scales on the back and sides of either of our non-venomous Snakes, we shall find there are nineteen of them. In the Viper there are twenty-one rows—rarely nineteen or twenty-three. Each one of these scales is marked with a tiny pit which appears to coincide with the end of a nerve fibre, so that one may say the sense of touch resides in every separate scale. The head is less distinct from the body than is the case in the Grass Snake; and the slender tail is one-fourth of the entire length in the male and one-sixth in the female.
The Smooth Snake is found throughout the greater part of Europe.
Viper or Adder(Vipera berus, Linn.).
At a superficial glance the Viper is quite distinct from our other Snakes. Instead of the long, gracefully tapered body of these, the Viper is short and thick in the body with a short tail. So far as the length is concerned, the average Viper is less than two feet. A few exceptionally large females have been recorded measuring two feet eleven inches; but the female is always slightly longer than the male—usually about an inch more. Two feet three inches may be regarded as the ordinary maximum for a female. The head is flatter above, and it broadens behind the eyes, so that it is very distinct from the body; further, the shields on the head are very much smaller than the corresponding plates of the Grass Snake. The iris of the eye is coppery-red, and the pupil is vertical—which usually denotes nocturnal habits, but the Viper is active by day as well as by night, and is fond of basking in the sunshine.
Respecting colour, there is a considerable range of variation, much of it sexual; but, generally speaking, it may be said to be some tint of brown, olive, or grey, and this ground colour may be so dark that the darker markings are scarcely perceptible on a cursory view. Along the sides there are whitish spots, sometimes reduced to mere dots. The brown, red-brown, or olive males have black markings; the grey or whitish males are marked with brown or black, and have the underside black. The throat is black, or whitish with scales spotted or edged with black.
The females if brown or brick-red have dark brown or red markings; olive females have brick-red bands or spots. The yellowish-white chin and throat are sometimes tinged with red. The eyes of the female are smaller than those of the male.
The markings are subject to a good deal of variation as well as the ground colour. The usual wavy or zigzag line down the centre of the back, with a series of spots on either side, may bebroken up into oval spots; and the characteristic pair of dark bars on the head may form either aΛor anΧ. The broad shields which cover the lower surface may be grey, brown, bluish, or black, or bluish with triangular spots of black, sometimes with white dots along the margins. Below the end of the tail the colour is yellow or orange. Specimens have been recorded almost entirely of a rich black, the excepted portion being the whitish underside of the head and throat.
The usual haunts of the Viper are sandy heaths, dry moors, the sunny slopes of hills and hedgebanks, bramble clumps, nettle beds, heaps of stones and sunny places in woods; but we have also found it in heathy and grassy places that were distinctly and permanently wet. For food they appear to prefer small mammals such as mice, shrews and voles, young weasels; but also take birds, lizards, slow-worms, frogs, newts, and large slugs. The young subsist for a time on insects and worms.
The Viper retires in autumn to a hollow under dry moss among the heather, under faggot stacks or into the discarded and leaf-covered ground nests of birds. They reappear about April, and may then be seen coiled on a sunny bank, apparently more concerned to absorb heat than to find food. They pair at this season, and the young (varying from five to twenty) are born in August or September. In this species, again, the eggs are retained until fully developed, and when the young see the light they are coiled up tightly in a thin, transparent membrane, which usually breaks during the process of birth. They measure from six to eight inches, and are at once independent.
The hoary old legend about the mother Viper opening her jaws to afford sanctuary to her young in time of danger has probably arisen from some occasional acts of cannibalism. It presupposes what is not true of any of our reptiles—that the young remain with their parent. They all begin life equipped for independence, and act accordingly.
The Viper is not so amenable to a life of captivity as ourother Snakes. It is not amiable, indeed its temper may be described as short and sulky, which it displays by refusing all offers of food; most captive Vipers die of starvation, the "hunger strike" being their effective protest against the deprivation of liberty. On being captured they are always ready to bite; but in a state of freedom the Viper is not the aggressive monster that is popularly supposed. It seems to depend largely upon its inactivity for escaping observation, but when it knows it has been discovered its immediate impulse is to seek cover. Accidents from Viper bites are rare in this country, where people go about well shod, and there are very few cases of authenticated death from this cause. On the Continent, however, such cases are frequent; and it is suggested that in the warmer parts of Europe, where bare feet are more numerous, the Viper's venom may also be more active than it is here. It is the toes or fingers that are most likely to be bitten, for the Viper's mouth is not large enough to enable it to bite the larger parts. The mechanism by which the poison is introduced into the blood of its victim has been briefly described onpage 146.
Lighter brown snake, dark brown wavy pattern on back, side spots; rocks and dry grasses.Pl. 96.][L 156.Viper or Adder.Vipera berus.View Larger Image Here.
Pl. 96.][L 156.Viper or Adder.Vipera berus.
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Male frog; vocal sacs below jaw and behind ear inflated to size of large peas.Pl. 97.][L 157.Edible Frog.With vocal sacs inflated in "singing."View Larger Image Here.
Pl. 97.][L 157.Edible Frog.With vocal sacs inflated in "singing."
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It must not be supposed from the foregoing remarks that we deprecate caution in dealings with the Viper; but we do desire, if possible, to dispose of that senseless fear that is unworthy of man. If the victim is in bad health the bite of the Viper may involve very unpleasant consequences—even death, but this is much more likely to follow from the sting of a gnat! In case of a bite from this species, the approved treatment is to suck the wound thoroughly and apply oil to it. The rustic remedy approved by quack doctors is an oil prepared from the Viper's own fat—"a hair of the dog that bit you" sort of cure. A ligament above the wound will prevent the poison spreading; and the blood may be made alkaline by the internal administration of ammonia. The popular idea in many parts is that the reddish-coloured Vipers have more virulent poison than theothers, but there does not appear to be any good grounds for this differentiation.
The Viper is found in all parts of Britain, but is not known in Ireland.
Frog(Rana temporaria, Linn.).
With the Common Frog, popularly classed as a Reptile, we commence acquaintance with the zoological class Batrachia, creatures that begin life at a much lower stage of development and have to pass through a fish-like larval form before attaining to any likeness to their parents. The Reptiles get through these developmental stages whilst they are still in the egg; they never have water-breathing organs. The Batrachians or Amphibians are clothed with soft skin which is not protected by armour plates or scales as seen in the Lizards and Snakes, but through which they are able to oxygenate the blood. The Frogs, Toads, and Newts constitute a class intermediate in structure and development between the Fishes and the Reptiles. Our native species represent the two orders—Ecaudata (tailless), including the Frogs and Toads; and Caudata (tailed) comprising the Newts.
Everybody knows the Frog as well as they know any of the backboned animals, and every youngster even is familiar with the main facts of its development, from the jelly masses of eggs in the pond early in spring, through the tadpole stage to the attainment of four legs and wonderful leaping powers. It is common knowledge that he has a moist, smooth skin (the supersensitive erroneously say "slimy") of yellowish ground colour overlaid with streaks and spots of brown. There is a big patch of brown behind each eye, and the long hind legs have cross-bars of the same colour. The ground tint of the Frog varies in different individuals according to the situation in which we may find them; for the pigment cells of the skin expand and contract under the influence of varying intensitiesof light reflected from the surroundings, causing colour changes much after the manner of those of the Chameleon, though less marked.
Broad head, rounded muzzle, long pelvis, very short forelimbs, lengthened rear limbs.Skeleton of Frog.View Larger Image Here.
Skeleton of Frog.
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The Frog's forelimbs are very short compared with the hind pair, and the four moderate-sized fingers are not connected by webs; whereas, the hind limbs have their several bones lengthened, and the abnormal lengthening of those of the ankle gives the legs the appearance of having a supplementary joint. The leg is one and a half times the length of head and body. The foot has five long toes connected for half their length by a "web" of skin which constitutes a very efficient paddle when the Frog is in the water. Of these hind toes the fourth is considerably longer than the long third and fifth.
The Frog's head is as broad as it is long, the muzzle rounded,and the horizontal gape of the mouth extends back beyond the eye. The prominent eyes are perched up on the forehead, and have a fine golden iris and a horizontal pupil. The Frog differs from the Snakes and agrees with the Lizards in having eyelids; he has also, like the Birds, an additional lid—the nictitating membrane. There is a row of delicate teeth along the upper jaw, but none on the lower; there are others on the palate. The deeply notched tongue is attached by its base to the front part of the mouth, the tip far in towards the throat; in use it has to be suddenly turned over so that the tip is projected far beyond the muzzle. The large circular depression behind and below the eye is the drum of the Frog's ear.
The Frog has no neck, the base of his skull coming close to the collar-bones, and there are only a few pairs of very short apologies for ribs between the shoulders and the long pelvis which produces that steep incline at the rear of his back. He is clothed entirely with a smooth, soft skin, which is kept moist by the action of minute mucous glands distributed all over the body. A row of these glands of larger size forms a pale line running back from the eye on either side. The skin plays an important part in the oxygenation of the Frog's blood; and the experimental physiologists have shown that a Frog deprived of its lungs can carry on its respiration for a lengthened period through the skin alone. Owing to the absence of ribs he has to fill his lungs by swallowing air.
The male is less portly than the female, and he is further distinguished by having two pads on the first finger which in the breeding season become large rough cushions enabling him to hold his mate. In his throat there is a pair of vocal sacs enabling him to produce his love songs, and when these are in use their inflation causes a distension of the skin of the throat; but without these adjuncts the female manages to give answering croakings. When these duets are sung under water they produce some curious effects.
When the pairing season arrives—quite early, usually about the middle of March, but sometimes in February—all the Frogs that have just come out of hibernation select their mates. Any pool of water will do, however transient, and they often make mistakes in this matter, their egg-masses being left high and dry when the waters dry up. The eggs are deposited in a mass of a thousand to two thousand at the bottom of the water, and at first they are only about a tenth of an inch in diameter, but the gelatinous covering absorbs so much water that they swell up to a third of an inch. There is a corresponding lightening of the mass, which floats to the surface and is available for observation. Each of the little jelly-spheres is seen to have a black centre—the egg proper—with a white spot on the lower side. If the spring is an average one, in about four weeks' time the black specks will have developed into brown larvæ or tadpoles, and having escaped from the egg these will be clinging to the remains of the jelly mass by means of a pair of suckers on the underside of the head. There are at present no indications of limbs—head, body and tail, like those of a fish, merge one into another. Even the gills are not yet developed, though what we may term the buds of them are seen on the bars separating the slits behind the head on each side. These buds soon expand into gill-plumes through which the blood circulates, taking up oxygen from the water that passes between them. There is as yet no mouth, but this will soon open, and horny plates on its jaws will enable the tadpole to crop soft vegetable matter, upon which it subsists chiefly. Later on, the gill-plumes will be hidden by a flap which grows over them. The full series of stages in this development may easily be watched by keeping a few tadpoles in a glass of water with a little growing pond weed.
Ultimately, the limbs appear. Though all four develop simultaneously, the hind pairappearfirst, because the forelimbs are at first hidden by the flap which grew over the gills.After the disappearance of the gill-plumes, proper lungs are developed inside the body, and the animal changes from a fish-like water-breather to an air-breather, in preparation for a life on land. When all the legs are well out the form of the tadpole soon changes to that of the Frog, except that it has a long tail. You may read in some books that the tail is shed, but this is a mistake that no one could make who has watched day by day the evolution of the Frog from the tadpole. The tail isabsorbed; it gets smaller daily, until finally the hind body is rounded off and there is nothing left to indicate that it once ended in a tail. Ultimately the Frog may attain a length of head and body equal to four inches.
Yellowish frog, streaks and spots of brown; brown patch behind eye; brown cross-bars on long hind legs.Pl. 98.][L 160.Common Frog.Rana temporaris.View Larger Image Here.
Pl. 98.][L 160.Common Frog.Rana temporaris.
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Dense amount of dark spots in translucent gel; deposited on rocks and pebbles, near water plants.Pl. 99A.]Spawn mass soon after deposit.Development of Frog's Eggs.View Larger Image Here.
Pl. 99A.]Spawn mass soon after deposit.Development of Frog's Eggs.
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Translucent egg mass expanded several times; dark eggs observable at various depths.Pl. 99B.]Eggs apparent after absorption of water.Development of Frog's Eggs.View Larger Image Here.
Pl. 99B.]Eggs apparent after absorption of water.Development of Frog's Eggs.
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Tiny tadpoles visible in translucent egg mass.Pl. 99C.]Germs assume Tadpole form.Development of Frog's Eggs.View Larger Image Here.
Pl. 99C.]Germs assume Tadpole form.Development of Frog's Eggs.
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Larger tadpoles breaking apart translucent egg mass.Pl. 99D.]Tadpoles begin to hatch out.Development of Frog's Eggs.View Larger Image Here.
Pl. 99D.]Tadpoles begin to hatch out.Development of Frog's Eggs.
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Some tadpoles still inside egg mass; others swarming on top of it.Pl. 100A.]Immature Tadpoles on outside of egg-jelly.Early stages of Common Frog.View Larger Image Here.
Pl. 100A.]Immature Tadpoles on outside of egg-jelly.Early stages of Common Frog.
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Many tadpoles in flattening egg mass. A few still inside.Pl. 100B.]Tadpoles begin to leave. Egg-jelly decomposing.Early stages of Common Frog.View Larger Image Here.
Pl. 100B.]Tadpoles begin to leave. Egg-jelly decomposing.Early stages of Common Frog.
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Tadpole and tail; no limbs.Pl. 100C.]Rise and decline of tail, and development of limbs.[C]Early stages of Common Frog.View Larger Image Here.
Pl. 100C.]Rise and decline of tail, and development of limbs.[C]Early stages of Common Frog.
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Tadpole, tail, and rear legs.Pl. 100D.]Rise and decline of tail, and development of limbs.[D]Early stages of Common Frog.View Larger Image Here.
Pl. 100D.]Rise and decline of tail, and development of limbs.[D]Early stages of Common Frog.
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Very young frog; front and rear legs; longer tail.Pl. 100E.]Rise and decline of tail, and development of limbs.[E]Early stages of Common Frog.View Larger Image Here.
Pl. 100E.]Rise and decline of tail, and development of limbs.[E]Early stages of Common Frog.
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Young frog; front and rear legs; shorter tail.Pl. 100F.]Rise and decline of tail, and development of limbs.[F]Early stages of Common Frog.View Larger Image Here.
Pl. 100F.]Rise and decline of tail, and development of limbs.[F]Early stages of Common Frog.
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Olive-brown frog; brown ear-drum behind eye; dark spots on body; dark marbling of hind legs.Pl. 101.][M 161.Edible Frog.Rana esculenta.View Larger Image Here.
Pl. 101.][M 161.Edible Frog.Rana esculenta.
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Mr. E. S. Goodrich, F.R.S., has recently demonstrated that eggs obtained from a female Frog by dissection can be fertilised by the leucocytes or colourless corpuscles of the blood. He exhibited a fatherless Frog, so obtained, before the Linnean Society in November, 1918.
When all the tadpoles have become real little Frogs, with their legs sufficiently firm to enable them to indulge in hopping exercises, they still for a time venture no further than the very shallow water at the extreme edge of the pond, where they can walk partially submerged. Then one day there comes a heavy summer rain storm—a deluge on a small scale. Every little Frog then appears to hear the word "Go!" for with one impulse they all scramble out of the pond into the jungle of wet grass, they know not whither. If there is a road near, that is the place in which to form an idea of their prodigious numbers. The few wayfarers who may be hurrying along that road, looking for possible shelter from the pitiless rain, and seeing the Frogs hopping along much as the raindrops bounce, are quite prepared to declare that they came down from the clouds with the rain. Many persons who in the ordinary affairs of life would be regarded as reliable witnesses have testified that this is what happens. To them it seems a much more reasonable explanationof this sudden appearance—they term it a phenomenon—than the naturalist's statement that the Frogs had been waiting in the pond for the psychical moment to arrive for their dispersion—the time when the reeking herbage of many acres around would offer the safest conditions for their tender bodies to embark on the great adventure of life, their distribution over wide areas where they could carry out their proper function, the control of any inordinate increase in the insect population. For months they will crawl and hop invisibly among the lush grass and journey through the dense herbage of hedgebottoms and spinneys. Some will come under fences even into our gardens, to help us in an unequal warfare in which the gardener is always defeated by the insect, whether the bigger combatant admits it or not. Their food consists entirely of insects, slugs, and worms. In turn the Frog constitutes the food of many larger animals, including fishes, birds, snakes and weasels. The winter is spent embedded in mud at the pond-bottom, or in damp holes in the earth.
The Common Frog is distributed widely all over Britain, but is only of local occurrence in Ireland. Abroad it ranges over Central and Northern Europe as far as Sweden and Norway, and eastward to Mid-Asia.
Edible Frog(Rana esculenta, Linn.).
Although the Common Frog is the only species that is really native in Britain, another one—the Edible Frog, a Continental species—has been naturalised in the Eastern Counties of England since the early part of the nineteenth century, when Mr. Geo. Berney brought about 1500 specimens from France and Belgium and turned them loose in the Fens, in the neighbourhood of Stoke Ferry, where they are no longer plentiful, though they occur locally in various parts of Norfolk. A few years later (1843) Mr. Thurnall discovered the species in theCambridgeshire Fens at Foulmire—a great distance (30 to 40 miles) from Stoke Ferry. Bell says his father had noted the presence of these Foulmire frogs, under the name of "Whaddon Organs," about the middle of the eighteenth century; so that it appeared that Mr. Berney had "taken coals to Newcastle"—in other words, had introduced the Edible Frog to a part of England where it already existed. In 1884 Dr. G.A. Boulenger discovered that the Foulmire frogs were of the Italian form ofRana esculentaknown as the varietylessonæ, which made it doubtful whether they could be travelled descendants of Mr. Berney's frogs. So it was suggested that they were a survival from an introduction by the Romans—who are always dragged in to help out doubtful cases.
The difference in the French and Italian forms is mainly one of colour, the type being a beautiful grass-green, whereaslessonæis olive-brown. But it has since transpired thatlessonæis not restricted to Italy as Boulenger thought, for he has more recently discovered it in Belgium and near Paris, and it has been recorded from parts of the former Austrian and German Empires. Such differences as there are in the two forms are not fundamental, and the brown tint of the Foulmire examples may be due to their environment. Fresh importations from the Continent have been liberated in recent years in Hampshire, Surrey, Oxfordshire, and Bedfordshire.
The Edible Frog attains to a rather larger size than the Common Frog. It is usually without the dark patch extending from the eye to the shoulder, and the markings of the body—especially the bright yellow and black marblings of the hinder parts—are darker and bolder. There is usually a light yellow or green line running down the middle of the back from the muzzle to the hinder extremity. The most distinctive feature, however, is restricted to the male sex: at the hinder angle of the mouth, just below the ear, are external vocal sacs which, when the owner is inclined to be melodious, become distendedwith air to the size of large peas, giving him a very quaint appearance. The croak differs from that of the Common Frog, and has been described as "more of a loud snore, exactly like that of the Barn Owl;" but this probably refers to the vocal efforts of the female, for Bell says it is so loud and shrill as to have obtained for the frogs the names of "Cambridgeshire Nightingales" and "Whaddon Organs." The males continue to "sing" after the breeding season is past, particularly on warm moonlight nights, when they may be heard for over a mile when the choir consists of several hundred voices. The notes are "Brekeke, gwarr, ooaar, coarx."
To return to a description of the Edible Frog. Full-grown examples measure from two and a half to four inches of head and body; the females larger than the males. The head is more slender than in the Common Frog, and the brown eardrum is two-thirds of the diameter of the eye. The teeth on the palate form two oblique lines; and there is a pair of glandular folds behind the eye. The ground colour of the upper parts ranges from dull brown through olive to bright green, with dark brown or blackish spots on the back and larger patches of similar tint on the limbs. There is usually a bronzy-brown line along each side of the back, in addition to the central one already named. The back of the thigh is always spotted with black and white or yellow. Though the thigh of the Common Frog is barred or blotched, it never bears these additional spots. The coloration generally is much brighter where the vegetation is light than in dark swamps with sombre vegetation.
The developmental history of the Edible Frog from the egg to the loss of the tadpole tail follows much the same course as that of the common species, and it is not necessary to recapitulate it. The eggs are more numerous, one female producing from five to ten thousand. The tadpole condition lasts three or four months. Full-grown tadpoles are about two and a half incheslong, of which more than an inch and a half is tail. The frog that has just got rid of his tail measures only half an inch. The young frogs are not such wanderers as their Common cousins, but remain in the vicinity of their birthplace, unless the pond dries up. They like to bask in the sun and wait till their food comes within range of their extensible tongues. They become mature between the fourth and fifth years.