TOO

ICHTHYOLOGY.

to the glass. They had a motion with their mouths, however,which shewed that they were not perfectly dead. On uncover-ing the vessel, they revived in two or three hours, and were per-fectly well next morning; at which time those in the exhaustedwater were also recovered. The vessel containing these last beingput under the receive!- of an air-pump, and the air exhausted,thev all instantly, died. They continued, at top while the air re-mained exhausted, but sunk to the bottom on the admission of theatmosphere. The use of air to fishes is very difficult to be ex-plained ; and indeed their method of obtaining the supply of whichthey stand constantly in need, is not easily accounted for. Themotion of the gills in fishes is certainly analogous to our breathing,and seems to be the operation by which they separate the air fromthe water. Their manner of breathing is as follows : the fish firsttakes a quantity of water by the mouth, which is driven to thegills; these close, and keep the water which is swallowed fromreturning by the mouth, while the bony covering of the gills pre-vents it from going through them till the animal has drawn theproper quantity ot air from it: then the bony covers open, andgive it a free passage; by which means also the gills are againopened, and admit a fresh quantity of water. If the fish be pre-vented from the free play of its gills, it soon falls into convulsions,and dies, Hut though this is a pretty plausible explanation of therespiration of fishes, it remains a difficulty not easily solved whatis done with this air. There seems to be no receptacle for con-taining it, except the air-bladder or swim ; which, by the gene-rality of modern philosophers, is supposed not to answer any vitalpurpose, hut only to enable the fish to rise or sink at pleasure. !

The Air-Bi.adder or Sound, is a hag filled with air, composedsometimes of one, sometimes of two, and sometimes of three divi-sions, situated towards the hack of the fish, and opening into theback of the fish, and opening into the maw or the gullet. Theuse of this in raising or depressing the fish, is proved by the fol-lowing experiment. A carp being put into the air-pump, and theair exhausted, the bladder hursts by the expansion of the air con-tained in it; after which the fish can no more rise to the top, hutever afterwards crawls at the bottom. The same thing also hap-pens when (he air-bladder is pricked or wounded in such a man-ner as to let the air out; in these cases also the fish continues atthe bottom, without a possibility of rising to the top. From thisit is inferred, that the use of the air-bladder is, by swelling at thewill of the animal, to increase the surface of the fish’s body, andthence diminishing its specific gravity, to enable it to rise io the

top of tile water, and to keep there at pleasure. On the contrary,when the fish wants to descend, it is thought to contract the air-bladder ; and being thus rendered specifically heavier, it descendsto the bottom. Ancient zoologists were of opinion, that the air-bladder In fishes served for some purposes essentially necessary tolife ; and Dr. Priestley also conjectures, that the raising or de-pressing the fish is not the only use of these air-bladders, hut thatthey also may serve some other purposes in the a-couoiny of fishes.There are many arguments indeed to be used on this side 6f thequestion : the most conclusive of which is, that all the cartilagi-nous kind of fishes want air-bladders, and yet they rise to the top,or sink to the bottom, of the water without difficulty ; and thoughmost of the eel-kind have air-bladders, yet they cannot raise them-selves in the water without great difficulty. Fishes are, in general,the most voracious animals in nature. In most of them, the mawis placed next the mouth ; and though possessed of no sensibleheat, is endowed with a very surprising faculty of digestion. Itsdigestive power seems, in some measure to increase in proportion,to the quantity of food with which the fish is supplied. A singlepike has been known to devour 100 roaches in three days. What-ever is possessed of life, seems to he the most desirable prey forfishes. Some that have very small mouths, feed upon worms, andthe spawn of other fish ; others whose mouths are larger, seeklarger prey ; it matters not of what kind, whether of their ownspecies, or any oilier. Those with the largest mouths pursue almostevery thing that has life ; and often meeting each other in fierce op-position, tlie fish with the widest throat devours its antagonist, andcomes off victor. As a counterbalance to this great voracity,fishes are incredibly prolific. Lcwenhoeck assures us, that thecod spawns above nine millions in a season. The flounder com-, monlv produces above one million, and the mackavel above300,000. Scarcely one in 100 of these eggs, however, brings forthan animal: they are devoured by all the less try that frequent theshores, by waterfowls in shallow waters, and by the larger fishesin deep waters. Such a prodigious increase, if permitted to cometo maturity, would overstock nature ; even the. ocean itself wouldnot he able to contain, much less provide for, one-half of its inha-bitants. But two wise purposes are answered by this amazing in-crease ; it preserves the species in the midst ot numberless enemies, and serves (o furnish the rest with a sustenance adapted toI their nature. And thus the purposes of the Creatin' and Up-holder of all things are, in this purt of his works, fully accom-plished.

ICIITIlYOMANCY, [from lx®es, a fish, and pamtu, divi-(nation,] in antiquity, the art of divining by inspecting the entrails 1of fishes.

ICHTH YOPFIAGI, [from '%Qvi, fish, and faynv, to eat,] Fish-Eaters, a name given to several nations who lived wholly onfishes.

ICIITI1YOPIITHALMITE, in mineralogy, a stone foundin Sudermania, colour yellowish ; specific gravity 2.5 nearly ;froths and melts into an opaque head, before the blow-pipe. Il«ecurs crystallized and massive, and it is thought to consist of

Silica.52.0

Lime.24.5

Potass. 8.1

Water.15.0

Other matter...... 4

too

TCHTIIYPERIA, in natural history, a name given by Dr.Hill to the bony palates and mouths of fishes, usually met witheither fossile, in single pieces or fragments.

ICKWOKTI1, a town of Suffolk, near Bury, 23 miles N. W.bv N. of Ipswich, and 74 N. N. E. of London . Lon. 1. 0. E.L'at. 52. 22. N.

ICOLMK1LL, or I-COLUMB-K1LL, a celebrated id: » ! ofScotland , and one of the IIei;ride£ : called also I, IIY, Hit, and

anciently Iona: famous for the monastery, founded in it, by St.Colnmba.

ICONIUM , in ancient geography, the capital city of Lycaonia:n Asia Minor, now cabl'd C'ogni.

ICONOCLAST M, ICONOCLASTF.S, or the ICONO-CLASTS, arc titles which the church of Rome gives to all whoreject the use of matters. Not only (he reformed, but some ofthe eastern churches, are called leonoclastes, and esteemed byi them heretics, as opposing (lie worship of the images of God andthe saints, and breaking their representations in churches. Theopposition to images began in Greece under the emperor Bar-danes, soon after the commencement of the eighth century, whentlie worship of them became common. See .(make. But the tu-mults occasioned by it were quelled by a r< volution, which in713, deprived Bardanes of the imperial throne. The dispute,however, broke out with redoubled fury under Leo the lsaurian,who issued out an edict in 726, abrogating ,he worship of images.’Phis edict occasioned a civil war, which broke out in the islands, of the Archipelago , and by the suggestions of the priests andmonks, ravaged a part of Asia, ami akerwards rear lied Italy .The civil commotions in Italy were chiefly promoted by Hu: Ho-; man pontiffs, Gregory l. and 'll. Leo was excoimminieati d, and: his subjects in the Italian provinces, rising in arms, cither innssa-i cred or banished all the emperor’s officer 1 .;. Leo assembled 11j council at Constantinople In 730, which degraded Germamis, the: bishop of that city, who was a patron of images : lie ordered all thej .iiiiagf s