Page:Popular Science Monthly Volume 29.djvu/261

Rh in the water. This mucous line is made up of rows of pores, which communicate with the slime-secreting glands. Leydig discovered that each of these oil-producers had its own nerve, thus constituting a series of sense-organs. And very delicate is their sense, as by them the fish gauges the weight of the water-mass, also the direction and resistance of currents. But associated with these nerves arranged in tufts, or buttons, are air-cells, hence it seems certain that the fish is able to appreciate vibration in water, whose wave-lengths are larger than are those of sound. The faculty of appreciating the waves of light, we call seeing, and similarly of sound, hearing, whose waves are much larger than those of light. But our scaly subject is endowed with a third wave-measuring sense, in which possession it out-paragons "the paragon" himself. It can appreciate the trills or waves of water vibration, and of this faculty our language has no word to express the name.

Now, these oil-yielding tubes above described may get clogged, or the glands become torpid. Here, then, are sense-organs to declare the state of affairs. Hence arises the necessity for the animal either to clean off its body armor, or to stimulate into activity the indolent organs. And, in fact, in other ways, fishes have their own eczema, or diseases of the skin. Sometimes there is a blistering or deterioration of the cutis, and sometimes a species of Saprolegnia, a fungous parasite, sets up a floculentflocculent [sic] growth on the cuticle. For any of these instances friction is the only remedy, and its exercise is unquestionably pleasant to the fish.

But how can a fish scratch itself? Sometimes in the way of Cushie, as when she rushed through the evergreens. So a fish will often dart through a dense clump of soft water-weeds. But this amounts to little else than a gentle titillation. The scaly sheath is not to be cleansed so easily. I have seen the performance many times, and by several species, but none have so much interested me in this respect as the sunfish. Take the one best known to the pin-hook anglers, and often called "pumpkin-seed." There is a bowlder with a smooth, clean surface. The fish is steady; its big eyes seem of a sudden to glow with a blue light. Every fin is set, even to the dorsal, which bristles with its keen spines. The fish seems aiming for that stone. The propulsion must come from the caudal and the side fins, but mostly from the former. All these give a simultaneous blow against the water; at the same time, as if it were in the way, the top-sail—that is, the dorsal—falls and is snugly reefed. All this is done in a moment, and such the force that the fish truly darts, threatening to butt its nose against the rock. The speed is high, but, just ere the rock is reached, there is a marvelously sudden bend of the body, the most convex point being the exact spot which is to be scratched. Though very rapid, so well-timed is the movement, and so nice the adjustment of the position, that the pressure or amount of rub or friction is correctly received, and the