SCRATCHING IN THE ANIMAL KINGDOM. 249 



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 or- 

 gans. 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 floculent 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 lit- 

 tle 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 sun- 

 fish. Take the one best known to the pin-hook anglers, and often 

 called "pumpkin-seed." There is a bowlder with a smooth, clean sur- 

 face. 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 propul- 

 sion 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 marvel- 

 ously 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 



