In Opostomias micripnus, a dark black fish living at a depth of over 2,000 fathoms, there are two rows of ocellar organs running down the sides of the body from the head to the tail. In the living animal they are said to shine with a reddish lustre. In addition to these, the conspicuous organs, there are `groups` of fifty, a hundred, or even more very much smaller organs situated on the sides and back of the fish, each of which is lenticular in shape and consists of a number of short polygonal tubes containing a granular substance with rounded bases resting on the subjacent tissue. The whole organ is covered 79by a simple continuation of the cuticle of the body-wall. The granular substance contained in the tubes is most probably the seat of luminosity.
In one of the 'cat-fishes'—the Aspredo—the mother carries the eggs about with her, and this is managed in a very remarkable way. Just at the time she lays her eggs, the skin of the under surface of her body becomes swollen and spongy, and into this she presses her eggs by lying on them. Here, snugly sheltered, they remain till hatched!
Thus, certain fishes related to the wonderful Anabas—the perch that climbs trees!—make nests of bubbles, in which the eggs are placed! The Gorami and the beautiful little 'paradise-fish', for example, built floating nurseries of this kind, the bubble-raft being made by the male. In the case of the paradise-fish these bubbles are blown so that the enclosed eggs are raised above the level of the water, where they remain till hatched! This raft, although it has been seen many times by travellers, is so frail that it cannot be preserved, and has never yet been drawn by an artist, so that we can only show the fish that makes it.
The male stickleback, as many of you may know, builds a wonderful nest, in which, when finished, he invites his chosen mate to lay her eggs. As soon as these precious treasures have been entrusted to his care, he makes himself their sole guardian, forcing currents of fresh water through the nest by the violent fanning motion of his breast-fins, and driving away all that come near. Strangely enough, he has to exercise the greatest care to keep out his mate, who would eat every single egg if she could but get the chance!
In the 'butter-fishes' or 'gunnels' which are found round our coasts, the eggs are rolled into a ball, and jealously nursed by the parents, each in turn coiling its body round the mass, and so protecting it from injury
Drawings by Professor Grassi, of Rome, of the young of the common Eel and its metamorphosis. All of the natural size. The uppermost figure represents a transparent glass-like creature—which was known as a rare “find” to marine naturalists, and received the name Leptocephalus. Really it lives in vast numbers in great depths of the sea—five hundred fathoms and more. It is hatched here from the eggs of the common Eel which descends from the ponds, lakes, and rivers of Europe in order to breed in these great depths. The gradual change of the Leptocephalus into a young Eel or “Elver” is shown, and was discovered by Grassi. The young Eels leave the great depth of the ocean and ascend the rivers in immense shoals of many hundred thousand individuals, and wriggle their way up banks and rocks into the small streams and pools of the continent.
Female Stickleback Laying Eggs in Nest
Male Stickleback Watching Eggs in Nest
Female Stickleback about to Enter Nest
The electric eel. There are several species inhabiting the water, and which have the power of producing electric discharges by certain portions of their organism. The best known of these are the Torpedo, the Gymnotus, and the Silurus, found in the Nile and the Tiger.
In the Surinam eel, the electric organ goes the whole length of the body along both sides. It is able to give a very severe shock, and is a formidable antagonist when it has attained its full length of 5 or 6 feet.
1. The fertilised egg, shed in the gravelly bed of the river.
2. The embryo within the egg, just before hatching. The embryo has been constricted off from the yolk-laden portion of the egg.
3. The newly hatched salmon, or alevin, encumbered with its legacy of yolk (Y.S.).
4 and 5. The larval salmon, still being nourished from the yolk-sac (Y.S.), which is diminishing in size as the fish grows larger.
6. The salmon fry about six weeks old, with the yolk fully absorbed, so that the young fish has now to feed for itself. The fry become parr, which go to the sea as smolts, and return as grilse.
In all cases the small figures to the right indicate the natural size.