AMPHIBIANS are creatures midway between fish and reptiles, and are adapted for a life both on land and in water. They all possess arangements for breathing air dissolved in water, and in the adults true lungs are always developed. Their limbs are never in the form of fins, and the skin is usually soft and moist. Instead of drinking in the usual manner, they absorb moisture through the pores. Their respiration is of importance : all have gills in their early stages and lungs in later life. The higher forms develop two sets of gills and
when gills are kept throughout life it is the external set which is retained.
In all cases the lungs are of simple construction and when the gills are retained they are the principal breathing organs. The moist skin also plays an important part in the process. As a class, amphibians are universally distributed, but none of them are found in the sea. They are divided into those that live in fresh water and those that are mainly land-dwellers.
THE LEGEND OF THE SALAMANDERS
IN what are known as the Tailed Amphibians the larval tail is retained throughout life; such are the Giant Salamanders of Japan and China. In the past many strange ideas were current about salamanders. They were supposed to be able to pass unharmed through fire, and were held to be so poisonous that nothing could save anyone who was bitten by them. Actually, both these beliefs are groundless. They do, however,
exude a poisonous fluid from the skin which injures any small creature taking hold of them in its mouth, and possibly this protective moisture might enable them to pass quickly through a moderate fire.
Water Salamanders, or Newts and Efts, are lizard-like in shape with a flattened tail. The fore-feet have four toes and the hind-feet five. The Common Newt is abundant in the ponds and ditches of Britain and is about three inches long, brown above and orange spotted with black below. The Crested Newt is nearly twice as long. Only the male has a crest and in the breeding season is quite gay in colour. All newts are able to replace a lost member, such as a tail or a leg—a faculty which shows them to be rather low in the scale of life.
The true Land Salamanders are rather like the newts in bodily shape, but they have comparatively thick bodies and the tail is rounded instead of being flattened. In the case of the Common Spotted Salamander of Europe and North Africa the young, on leaving the mother, have external gills and are deposited in water. On the other hand, with the Black Salamander of the mountain districts of Central Europe, only two embryos are hatched at a time, and these are retained in the mother’s womb until development is far advanced. While inside the mother the embryos have very long external gills, but they do not leave the mother till these disappear, and they start their outside life as genuine land creatures.
Lastly there are those strange creatures the axolotls, of which all the known species—about twenty in number— are to be found in the United States and in Mexico. The name Axolotl is really only applicable to the larval form, which in some cases is never changed. When this is so, the creature is aquatic in habits. Should its surroundings, however, not be suitable to this mode of life, a terrestrial form is assumed, and this is known as an Amblystome. The reason for the arrested development of many axolotls is that they have inadequate thyroid glands. It has been discovered that artifical feeding of the thyroids will at any time produce this change.