CHAPTER I.

_LUNG-FISHES AND CHIMÆRAS._

BY W. P. PYCRAFT, A.L.S., F.Z.S.

Though amongst the lowest of the backboned animals, the Fishes are nevertheless an exceedingly interesting group, distinguished from all others by the possession of fins, which are divisible into two series,--an unpaired, ranged along the middle of the back and abdomen, and including the tail-fin; and a paired series, representing the fore and hind limbs of land animals. The body is either clothed with scales or naked, and, being perfectly sustained by the water, needs no support from the fins, which serve as balancing-organs.

In the brilliancy and beauty of their coloration fishes display a variety that cannot be excelled by any other animals. Furthermore, the coloration is often rendered still more beautiful from the fact that it can undergo rapid changes of hue. Frequently this coloration is of a protective character, causing the fish to harmonise with its surroundings, and so escape the observation of its enemies. The colours of living fishes can only, for the most part, be indicated in the present pages when a pattern exists by the formation of stripes or spots; but the wonderful variations in the form of the body will probably prove a revelation to many.

LUNG-FISHES.

The LUNG-FISHES are a peculiarly important group, inasmuch as they form a connecting-link between the class Fishes and the land-dwelling Amphibians--the class containing the Frogs and Toads and their allies. They are accorded this position mainly because, like Amphibians, they possess true lungs, which almost entirely replace the gills, the breathing-organs of other fishes.

One of the best known of the lung-fishes is the AUSTRALIAN BARRAMUNDI, or LUNG-FISH OF QUEENSLAND--the BURNETT or DAWSON SALMON of the settlers. It lives among the weeds at the bottom of muddy rivers, rising frequently to the surface to take in atmospheric air by the lungs, the gills alone being insufficient for breathing purposes. The flesh, which is salmon-coloured, is much esteemed as food. The adult fish is said to attain to a weight of 20 lbs. and a length of 6 feet.

Other lung-fishes, eel-like in form, occur in the rivers of Africa and South America. The African species is perhaps the better known of the two. On the approach of the dry season it buries itself in the mud at the bottom of the river, and when the latter becomes dry the mud hardens, holding the fish a prisoner till the return of the wet season several months later. A considerable number of these fishes have from time to time been dug out and sent to England enclosed in the mud into which they had retreated. The writer remembers assisting in the liberation of some during the last meeting of the British Association at Oxford. So hard had the prison-walls become that the mass had to be plunged into tepid water; this soon brought about a dissolution of the soil, and in a short time the fishes were swimming about as if in their native rivers. The African lung-fish is known also as the MUD-FISH; its American relative as the LEPIDOSIREN, or SOUTH AMERICAN MUD-FISH. In the American species, as in its African relative, the fins are whip-like in form; but the hinder or ventral pair, which correspond to the hind limbs of the higher vertebrated animals, are remarkable in that in the male they develop during the breeding-season numerous thread-like processes, richly supplied with blood, the function of which is as yet unknown.

The young, both of the African and South American mud-fishes, bear external gills closely resembling those of the tadpoles of the frog and other Amphibia; traces of these gills remain throughout life in the African form.

CHIMÆRAS.

Shark-like in their general characters, the CHIMÆRAS, now briefly considered, are nevertheless regarded as constituting a very distinct group of great antiquity.

The modern representatives of the group are few in number--five species in all. Of these, the species shown in the accompanying photograph and the SEA-CAT are remarkable for the possession of a movable tentacle on the snout. The under surface of this tentacle is armed with small spines, and fits into a hollow in the head. The first back-fin is supported in front by a strong spine, and can be depressed into a sheath in the body-walls. The teeth take the form of large plates closely united with the jaws, and studded with hardened points, or "tritors."

One species widely distributed in the Mediterranean and Atlantic is taken usually in deep water; it is the largest living species, often attaining a yard in length. Its occurrence is, however, very erratic, months elapsing without any being taken; at other times several will be caught in a few days. A closely allied fish is often exposed for sale in the Lisbon markets, where it ranks with the Sharks as a food-fish.

The egg of the BOTTLE-NOSED CHIMÆRA is perhaps the only egg with a mimetic resemblance to a foreign object. It is elliptical in form, and bordered by a fringe, so as to present a close resemblance to a piece of seaweed.

In the next chapter we begin the description of the great group of Fan- and Fringe-finned Fishes, which, briefly, embrace all fishes not grouped among the Lung-fishes, Chimæras, or Sharks. The anatomical characters used for the purpose of classifying this great group are not discussed here, save only in a few cases of prime importance, when features such as can readily be observed, without demanding an intimate knowledge of anatomy, are selected.

----