ICH 



ICO 



division at the extremity. In some cases, 

 those on the back of the fish are furnish- 

 ed with, membranaceous appendages, 

 simple, or palmated, and adhering to the 

 apex, or sides. The fins, according to 

 their position, are denominated dorsal, 

 pectoral, ventral, anal, or caudal. 



The skeleton of a fish is the assemblage 

 of bones which constitutes the frame- 

 work of its body. The number of these 

 bones is not uniform in each individual, 

 but varies according to age and species. 

 They may be conveniently divided into 

 those of the head, thorax, abdomen, and 

 fins. 



The muscles are an assemblage of small 

 bundles of fleshy fibres, partly red, and 

 partly whitish, enveloped in a common 

 membrane. The first of. these is called 

 the fleshy portion of the muscle ; the se- 

 cond {he tendon. Each muscle thus com- 

 posed is susceptible of contraction and di- 

 latation. The former is accompanied by 

 a visible swelling, hardening, wrinkling, 

 and shortening of the muscle, and the lat- 

 ter by its elongation, expansion, and re- 

 covery of its former softness and flexibili- 

 ty. Its force, in general, depends on the 

 quantity of fibrous matter which enters 

 into its composition, and its moving power 

 on the length and size of the fibres. 



The brain of fishes is a very small organ 

 relative to the size of the head. It is di- 

 vided into three equal lobes, of which the 

 two anterior are contiguous ; the third be- 

 ing placed behind, and forming the cere- 

 bellum. These three lobes are surround- 

 ed by a frothy matter, resembling saliva. 

 In this region, the optic and olfactory 

 Herves are easily discovered. 



The swimming, or air bladder,or sound, 

 is an oblong, white, membranous bag, 

 sometimes cylindrical, sometimes ellipti- 

 cal, and sometimes divided into two or 

 three lobes, of different lengths. It is 

 usually situated between the vertebrae and 

 the stomach, and included within the pe- 

 ritoneum. In some fishes it communicates 

 with the stomach, and in others with the 

 oesophagus. The flat fishes are unpro- 

 vided with this organ. 



The intestines, which in man are placed 

 transversely, have a longitudinal position 

 in fishes, and are all connected with the 

 substance of the liver. They are in ge- 

 neral very short, making only three turns, 

 the last of which terminates in a common 

 outlet or vent. The appendices, or se- 

 condary intestines, are very numerous, 

 composing a group of worm-like proces- 

 ses, all ultimately terminating in two large 

 canals, opening into the first intestine, in- 



to which they discharge their peculiar 

 fluid. We shall, under the word PISCES, 

 give an account of the several functions 

 peculiar to this class of animals. 



ICHTHYOPHTHALMITE, in mine- 

 ralogy, a stone found in Sudermania, of a 

 yellowish colour : it occurs massive, and 

 crystallized. Specific gravity 2.5 nearly. 

 Before the blow-pipe it froths, and melt* 

 in'O an opaque head. It is supposed to 

 consist of 



Silica 52.0 



Lime 24.5 



Potash 8.1 



Water ..... 15.0 



Loss 



100 



ICONOCLASTS, in church history, aa 

 appellation given to those persons, who, 

 in the eighth century, opposed image- 

 worship ; and is still given by the Church 

 of Rome to all Christians who reject the 

 use of images in religious matters. 



ICOSAHEDRON, in geometry, a re- 

 gular solid, consisting of twenty triangu- 

 lar pyramids, whose vertexesmeet in the 

 centre of a sphere, supposed to circum- 

 scribe it; and, therefore, have their height 

 and bases equal ; wherefore the solidity 

 of one of those pyramids multiplied by 

 twenty, the number of bases, gives the* 

 solid content of the icosahedron. See 

 BODY. 



ICOSANDRIA, in botany, the name o 

 the twelfth class in the Linnzean system, 

 consisting of plants with hermaphrodite 

 flowers, furnished with twenty or more 

 stamina, that are inserted into the inner 

 side of the calyx, or petals, or both. By 

 this last circumstance, and not by the 

 number of stamina, is this class distin- 

 guished from the class polyandria, in 

 which the number of stamina is frequent- 

 ly the same with that of the plants of the 

 class icosandria, but they are inserted, 

 not into the calyx or petals, but into the 

 receptable of the flower. The icosandrit 

 furnishes the pulpy fruits that are most 

 esteemed, such as apples,plumbs,peaches, 

 cherries, &c. whereas the polyandria are 

 mostly poisonous, as the aconite, colum- 

 bine, larkspur, hellebore, and others. 

 The species of the icosandria have a hol- 

 low flower-cup, composed of one leaf, to 

 the inner side of which the petals are 

 fastened by their claws. I& thja class 



