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AND SOLD BY ALL THE BOOKSELLERS IN THE UNITED KINGDOM.

1816.

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ENCYCLOPÆDIA PERTHENSIS.

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NEREIS, in zoology, a genus of animals belonging to the order of vermes mollufca. The body is oblong, linear, and fitted for creeping; it is furnished with lateral pencilled tentácula. There are 11 fpecies, of which the most remarkable are the five following:

1. NEREIS CERULEA, the blue nereis, inhabits the ocean; where it deftroys the ferpulæ and teredines. See Plate CCXLVI, fig. 1.

2. NEREIS CIRROSA, the waving nereis. See fig. 2. The body is red, lumbriciform, with 65 notches, furnished on both fides with two rows of briftles. At each fide of the head ten filaments, at the fides of the mouth many, twice as long as the former. It dwells in Norway, on rocks at the bottom of the fea. It vomits a red liquor, with which it tinges the water.

3. NEREIS GIGANTEA, the giant nereis, is a peculiar fpecies of those large worms that make their way into decayed piles driven down into the fea, which they bore through and feed upon, whence they are called fea avorms. From head to tail they are beset on either fide with fmall tufts terminating in three points; which are like the fine hair pencils used by painters, and compofed of fhining briftles of various colours. The upper part of the body in this worm is all over-covered with small hairs. The rings of which it is formed are closely preffed together, and yield to the touch. The 3 rows of fmall tufts ferve instead of feet, which it ufes as fifh do their fins. See fig 3. 4. NEREIS LACUSTRIS, the bog nereis. The body of the fize of a hog's fhort briftles, tranfparent, as it were articulated, and 'on either fide at every articulation provided with a fhort fetaceous foot; interiorly it seems to confift in a mannet of oval-shaped articulations, and a back formed by two lines bent backwards. See fig. 4. It inhabits marshes abounding in clay, where it remains under ground pushing out its other extremity by reafon of its continual motion. When taken out it twifts itself up. It is frequent in Sweden.

5. NEREIS NOCTILUCA, the nodilucous nereis, inhabits almost every fea, and is one of the caufes of the luminoufnefs of the water. Thefe creatures fhine like glow-worms, but with a brighter splendour, so as at night to make the element apVOL. XVI. PART I.

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pear as if on fire all around. Their bodies are fo minute as to elude examination by the naked eye. See fig. 5. It is fometimes called nereis phofpherans; and is thus defcribed by Grifelin: The head is roundish and flat, and the mouth acuminated. The two horns or feelers are fhort and fubulated. The eyes are prominent, and placed on each fide the head. The body is compofed of about 23 segments or joints, which are much less nearer the tail than at the head. These fegments on both fides the animal all end in a fhort cónical apex, out of which proceeds a little bundle of hairs; from under thefe bundles the feet grow in the form of small flexile fubulated fegments deflitute of any thing like claws. It is fcarcely two lines long, is quite pellucid, and its colour is that of water green. They are found upon all kinds of marine plants; but they often leave them and are found upon the furface of the water: they are frequent at all seasons, but efpecially in fummer before ftormy weather, when they are more agitated and more luminous. Their numbers, and wonderful agility, added to their pellucid and fhining quality, do not a little contribute to their illuminating the fea, for myriads of thofe animalculæ may be contained in the portion of a small cup of fea water. Innumerable quantities of them lodge in the cavities of the fcales of fishes, and to them probably do the fishes owe their noctilucous quality. "I have obferved with great attention (fays Barbut) a fish juft caught out of the fea, whofe body was almoft covered with them, and have examined them in the dark: they twist and curl themselves with amazing agility, but foon retire out of our contracted fight; probably their glittering numbers dazzling the eye, and their extreme minuteness eluding our refearches. It is to be obferved, that when the unctuous moisture which covers the fcales of fifhes is exhaufted by the air, thefe animales are not to be seen; nor are the fishes then noctilucous, that matter being perhaps their nourifhment when living, as they themselves afford food to many marine animals. They do not thine in the day-time, because the folar rays are too powerful for their light; however aggregate or immense their number." Their appearance is particular

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