পাতা:পদার্থবিদ্যাসার.djvu/১২১

1.10 Tut. To preserve them from being bruised or crushed by the presure of the water, and to guard them against the cold. Pup. How do they dart forward so nimbly in the water Tut, loy means of their tail, by the motion of which they push themselves forward. Pup. Of what use are the fins Tut. To keep them in equilibrium, or with their belly downward; to turn on either side, or to stop their progress. Pup. By what means do they rise or descend in the water 2. Tui. They are enabled to do this by an air-bladder, which they can dilate or contract at pleasure. Pup. How does that occasion their ascent or descent Tut. By expanding the bladder they become lighter than water, and by contracting it they become heavier. s pup. How are they supported Tut. They eat worms, and flies, and plants: and the large fish feed upon the smaller, of which there are immense numbers. - ' ' . Pup. Is not the spawn of some fish very numerous? Tut. The spawn of a perch will produce more than twenty-eight thousand fish: upwards of a million and