ICH 



ICH 



after a certain period they emerge in the 

 tate of complete ichneumons. 



I. glomeratus may be given as an ex- 

 ample of this process. The caterpillar of 

 the common white or cabbage butterfly, 

 which, in the autumnal season, may be 

 .observed to creep up some wall, &c. in 

 order to undergo its own change into a 

 chrysalis : but in the space of a day or 

 two, a numerous tribe of small maggots 

 will be seen to emerge from it, and im- 

 mediately proceed to envelope them- 

 selves in distinct, yellow, silken cases, the 

 whole forming a group round the cater- 

 pillar. These are the ichneumons glo- 

 meratus: they are black, with yellow 

 legs, and they usually make their appear- 

 ance in about three weeks from the time 

 of their spinning themselves up. Some 

 of the ichneumon genus pierce the skins 

 of newly -changed chrysalises of butter- 

 flies and moths, in which their larva re- 

 main during their own incomplete state. 

 Others are so minute, that the female 

 pierces even the eggs of moths and but- 

 terflies, and deposits her own in each. I. 

 seductor, has a yellow scutel ; tip and pe- 

 tiole of the abdomen and crenate band 

 on the fore-part yellow ; legs mostly yel- 

 low. This insect is found chiefly in Pavia; 

 it forms a nest of cemented clay, in chim- 

 neys and windows, divided into cylindri- 

 cal cells, in each of which is contained a 

 cylindrical, brown, lucid follicle, and in 

 this the larva, with frequently the carcase 

 of a spider, in which the insect had de- 

 posited her eggs. 



1CHNOGRAPHY, in perspective, tnl 



of any thing cut off by a plane 

 parallel to the horizon, just at the base 

 of it. 



IcHtfOGRAPHY, in architecture, .a de- 

 scription or draught of the platform or 

 pound-work of a house, or other build- 

 ing. Or it is the geometrical plan or plat- 

 form of an edifice or house, or the ground- 

 work of an house or building, delineated 

 upon paper, describing the form of the 

 several apartments, rooms, windows, 

 chimneys, &c. 



ICHJTOGRAPHY, in fortification, denotes 



the plan or representation of the length 



and breadth of a fortress, the distinct 



i parts of which are marked out, either on 



the ground itself, or on paper. 



ICHTHYOCOLLA. See ISINGLASS. 



ICHTHYOLOGY, is that part of natu- 

 ral history that treats of fishes. And fish- 

 es are animals having a heart with one 

 auricle and one ventricle, with cold red 

 blood, which inhabit water, and breathe 

 by means of gills. Most of the species 



are likewise distinguished by fins and 

 scales. Different naturalists have given 

 different systems ; we shall briefly notice 

 some of the principal, because we find 

 them perpetually referred to in works of 

 importance. Aldrovandus, about two hun- 

 dred years ago, distributed the fishes ac- 

 cording to the nature of their residence. 

 His first book treats of those that frequent 

 rocks ; the second is devoted to those 

 found near the shores, called littoral ; the 

 third, pelagian, &c. Willoughby formed 

 his system from his observation on the 

 anatomy and physiology of fishes; he was 

 followed by Ray, who fixed a series of' 

 genera. Artedi, the friend and country- 

 man of Linnaeus, has the merit of having 

 first traced the outlines of that classifica- 

 tion of fishes, which is now almost gene- 

 rally adopted. For, independently of the 

 cetaceous tribes, which are now generally 

 classed with the mammalia, his method 

 consisted of four orders, viz. 1. The mala- 

 coterygian, or those which have soft fins, 

 or fins with bony rays, but without spines. 

 2. The acanthopterian, those with spiny 

 fins. 3. The branchiostegous, corres- 

 ponding to the amphibia nantes of Lin- 

 naeus. 4. The chondropterygian, or those 

 which have not true bones, but only car- 

 tilages, and the rays of whose fins hardly 

 differ from a membrane. At first Linnaeus 

 adopted this method entirely, but he af- 

 terwards improved upon it ; and now, ac- 

 cording to his system, the orders have 

 been instituted from the situation, pre- 

 sence, or absence of the ventral fins. 



1. Such, .as are entirely destitute of 

 these fins are termed pisces apodes, apo- 

 dal or footless fishes. 2. The jugulares, 

 or jugular, are those which have ventral 

 fins, placed more forward than the pecto- 

 ral fins, or under the throat. 3. The tho- 

 racici, or thoracic, include those whose 

 ventral fins are placed immediately under 

 the pectoral fins, or on the breast. 4. The 

 abdominales, or abdominal, comprise 

 those whose ventral fins are situated be- 

 hind the pectoral fins, or on the abdomen. 

 4. There still remains a particular tribe, 

 denominated cartilaginei, which, as their 

 name imports, have a cartilaginous instead 

 of a bony skeleton. This tribe was by Lin- 

 naeus separated from the rest, on the mis- 

 taken idea, that the individuals which 

 compose it were furnished both with 

 lungs and gills, and should be ranked in 

 the class of amphibious animals. 



The genera-which pertain to the pre- 

 ceding orders are determined by the 

 number of rays in the bi-anchiostegous 

 membrane, the condition of the teeth, the 



