INS 



I NT 



pleted their growth, especially those of 

 mosses. 



INOPE'RCULAR {in, not, operculum, 

 a lid). A term applied to univalve shells 

 which have no operculum or lid. 



INOSCULA'TION (in, and osculum, 

 a little mouth). The union of vessels, or 

 anastomosis : the latter term, however, is 

 sometimes used to designate union hy 

 minute ramification ; the former, a direct 

 communication of trunks. 



INSCRIBED FIGURE. In Geome- 

 try, a circle is said to be inscribed in a 

 triangle or a polygon, when it touches all 

 the sides of these figures. A triangle or 

 a polygon is said to be inscribed in a 

 circle, when all the angles of the former 

 figures touch the circumference of the 

 latter. 



INSE'CTA {insecius, divided into seg- 

 ments). Insects ; a class of articulated 

 animals with six feet, which breathe by 

 tracheae, have a dorsal vessel for circu- 

 lation, one pair of antennae, compound 

 eyes, generally pass through a distinct 

 metamorphosis and acquire wings, and 

 are oviparous with the sexes distinct 

 Burmeister divides them as follows : — 



1. Insecta ametabola. Insects which 

 do not undergo metamorphosis. The 

 larva resembles the perfect insect, but 

 is without wings. The pupae of such 

 species as have wings in their imago 

 state possess rudiments of those organs. 

 The pupa runs about and eats. To this 

 division belong the orders Hemiptera, 

 Orthoptera, and Dictyoptera. 



2. Insecta metabola. Insects which 

 undergo metamorphosis. The larva is a 

 worm either with or without legs. The 

 pupa is quiet ; or, if it moves, it does not 

 eat. To this division belong the orders 

 Neuroptera, Diptera, Lepidoptera, and 

 Coleoptera. 



INSECTI'VORA {insecta, insects, 

 vara, to devour). A group of mammi- 

 ferous animals, considered by Cuvier as 

 a family of the great carnivorous order, 

 and characterized by their molar teeth 

 being studded with sharp points, which 

 enables them to devour insect prey. 

 They comprise the mole, the hedgehog, 

 the shrew, &c. 



INSE'PARABLE ACCIDENT. A 

 logical g,ccident, which cannot be sepa- 

 rated from the individual to which it 

 belongs, though it may from the species, 

 as for a person to be a native of London. 

 See Accident. 



INSESSO'RES {insideo, to sit upon). 

 Perchers; an order of Birds, the foot 

 181 



of which is especially formed for grasping 

 or perching— a peculiarity evinced by the 

 situation of the hinder toe, which is 

 invariably placed on the same level or 

 plane as those in front. 



INSOLA'TION {in, and «o/, the sun). 

 A term sometimes employed to denote 

 exposure to the sun for the purpose of 

 promoting the chemical action of one 

 substance upon another. 



INSOLUBI'LITY (in, not, solvo, to 

 loose). A property, resulting from co- 

 hesion, by which a substance resists so- 

 lution. 



INSPISSA'TION {in, and spissatus, 

 thickened). The process of making a 

 liquid of a thick consistence. 



INSTANCES, PREROGATIVE. Un- 

 der this term Lord Bacon cites all those 

 instances, or facts, which have a chief 

 claim to be noticed in the attempt to in- 

 terpret the laws of nature. He distributes 

 them into three classes, viz. those which 

 address themselves to the understanding, 

 those which assist the senses, and those 

 which conduce to practice. 



INSTINCT. The spontaneous impulse 

 by which animals perform certain ac- 

 tions. Under this term should be dis- 

 tinguished the instinctive faculty, which 

 leads the duckling, untaught, into the 

 water, and the chick, untaught, to avoid 

 the water ; and the instinctive motions, 

 or those involuntary actions which are 

 excited mediately through the nerves, as 

 the closing of the eye-lids, the act of 

 swallowing, &c. 



INSULATION {insula, an island). A 

 metaphorical term applied to a body con- 

 taining a quantity of electric fiuid, and 

 surrounded by non-conductors, so that it 

 is insulated, or its communication with 

 other bodies is cut off. 



INSU'RANCE. A per-centage paid 

 for insuring property from fire, &c. 

 When the charge is settled for any kind 

 of property, it is reckoned per cent, upon 

 the whole amount of it. The annual 

 payment is called the premium, and the 

 legal document, by which the securer is 

 insured from loss so long as he continues 

 to pay the premium, is called the policy 

 of insurance. 



I'NTEGER. Literally " whole ;" and, 

 hence, applied in arithmetic to a whole 

 number, as distinguished from a fraction. 

 INTEGRAL CALCULUS. That branch 

 of mathematical science which investi- 

 gates the processes by which a function 

 may be found such that its differential 

 shaJl be a given quantity. It was for- 



