I will only take two examples of true Estivation, one from Africa and the other from America. The first is the well known Lepidosiren, or mud-fish, a creature which has long been an enigma to zoölogists, as no one could say definitely whether it were a fish or a reptile. Professor Owen, however, states that the structure of its organs of smell proves that it is a true, though rather anomalous, fish. It is found in many parts of Africa, and inhabits the banks of muddy rivers, being plentiful in the Nile.
Nowadays, the systematic naturalists have changed its name and called it Protopterus, giving the old and equally appropriate name of Lepidosiren to an allied species which is found in the Amazon river and its tributaries. I have, however, retained the original name, and see no sufficient ground for altering it.
It is brownish grey in color, and eel-like in shape, but has four curious rudimentary limbs, apparently useless for locomotion, though they are seldom without movement. They are, in fact, soft single rays of the pectoral and ventral fins, which represent the limbs of beings more highly organized. Each ray carries a narrow strip of membrane along nearly the whole of its length.
Along part of the back there is a very soft fin, extending over the tip of the tail, and returning on the under surface of the body as far as the base of the hind limbs. The body is always covered with viscous slime, insoluble in water, and the creature seems to be able to secrete it as it is wanted.
Essentially predacious, it does not possess rank after rank of teeth, such as we see in the pike, and the wolf-fish, and the like, but is endowed with a most remarkable dental apparatus.
Instead of separate teeth, there is in each jaw what may be called a tooth-ribbon. Suppose that we imagine the dental matter, instead of being made into separate teeth, to be rolled out into a continuous ribbon, then “pleated” into folds like those of a ruff, and so set in the jaws. Then let us imagine the projecting edge of each tooth-ribbon to be as sharp as that of a chisel, and we can realize the formidable apparatus with which the mouth is armed.
These details are here briefly given, because without them the history of its estivation could not be understood.
That the Lepidosiren was carnivorous had long been known, but no idea was formed of its voracity until some living specimens were successfully reared in the Crystal Palace. One of them was placed in the large water basin which then adorned the center of the tropical department at the north end of the Palace, but which may now be seen in the open air between the Palace and the water tower.
Though confined in a tank, it contrived to escape into the basin, and straightway began to make havoc among the gold-fish. It swam gently under them, rose with open jaws, caught the fish just behind the pectoral fins, bit out a piece, its ribbon-like teeth cutting through scale, bone, and flesh, as if they had been shears, and sank out of sight with its prey. It never bit the same fish twice, and as long as it could find fish, declined to eat anything else.
As this mode of feeding involved a gold-fish for each mouthful, Mr. F. W. Wilson, who was then in charge of the Natural History Department of the Crystal Palace, had the tank emptied, and fenced off a portion with wire grating, so that the Lepidosiren could not get at the fish. The creature was then fed with frogs, which I have seen it eat; and by reason of the perpetual supply of food, it grew so fast that it attained a length of thirty inches and weighed six pounds and a quarter, a very giant of Lepidosirens, which seldom exceed eighteen inches in length.