Vietnam or Thailand ? Vote for the TOP Country of the Week !
Updated: May 3, 2025
He describes the various kinds of eggs, and, with still more surprising knowledge, shows us the little embryo cuttle-fish, with its great yolk-sac attached, in apparent contrast to the chick's, to the little creature's developing head. But there is one other remarkable feature that he knew ages before it was rediscovered, almost in our own time.
When hatched out and kept in water containing a very large quantity of air in solution, I found that sometimes alevins developed an air bubble in the yolk-sac. On developing this bubble they are unable to stay at the bottom as they usually do, but swim about on their backs at the surface, with part of the yolk-sac out of the water.
This is the umbilical or yolk-sac, and contains the nourishment upon which the little fish lives during the first stage of its life after it is hatched. This sac is gradually absorbed but until it is absorbed the young fish are called "alevins." At first the little fish do not require any food, but they generally begin to feed in about six weeks, and before the yolk-sac is completely absorbed.
Up to this time he had lived entirely on the provisions which his parents had left him, but henceforth he was independent and could take care of himself. He was no longer an embryo; he was a real fish, a genuine Salvelinus fontinalis, as carnivorous as the biggest and fiercest of all his relations. The cleft in his breast might close up now, and the last remnant of his yolk-sac vanish forever.
An effectual cure for this is to put the affected alevins into still water for about thirty-six hours. "Blue Swelling" of the yolk-sac is another disease from which alevins sometimes suffer, but I have never heard of any cure for this. Another, "paralysis," may be caused by lack of sufficient current and by insufficient aeration of the water.
He stayed in the gravel nearly a month, but his yolk-sac was gradually shrinking, and after a time it drew itself up into a little cleft in his breast and almost disappeared. There was nothing left of it but a little amber-colored bead, and it could no longer supply food enough for his growing body. There were times when he felt decidedly hungry.
There is no pursuit, for there is no escape; and we can only conclude that, as the new-born fish's first nourishment is the contents of the yolk-sac, partly outside, though still a portion of its body, so the first food of the young spiders is, if not themselves, the next best thing, each other.
Word Of The Day
Others Looking