INF 



[ 233 ] 



INS 



stomachs, the lowest class is there- 

 fore called Polygastrica. They are 

 the food of higher classes, particu- 

 larly of zoophytes. There is no 

 proper skeleton in the entire class 

 of animalcules called Polygastrica. 

 Some of the polygastrica exude on 

 their surface a secretion which 

 agglutinates, and lays hold of, 

 foreign particles floating in the 

 waters which surround them, and 

 thus form for themselves a partial 

 covering. The earthy matter, 

 however, is not their own produce. 

 Prof. Grant. 



Prof. Buckland observes, "We 

 are more perplexed in attempting 

 to comprehend the organization of 

 the minutest infusoria, than that of 

 a whale ; and one of the last con- 

 clusions at which we arrive, is a 

 conviction that the greatest and 

 most important operations of nature 

 are conducted by the agency of 

 atoms too minute to be either 

 perceptible by the human eye, or 

 comprehensible by the human un- 

 derstanding." 



Ehrenberg has ascertained that 

 the infusoria, which have heretofore 

 been considered as scarcely orga- 

 nized, have an internal structure 

 resembling that of the higher ani- 

 mals. He has discovered in them 

 muscles, intestines, teeth, different 

 kinds of glands, eyes, nerves, and 

 male and female organs of repro- 

 duction. He finds that some are 

 born alive, others produced by 

 eggs, and some multiplied by spon- 

 taneous divisions of their bodies 

 into two or more distinct animals. 

 Their powers of reproduction are 

 so great, that from one individual 

 a million were produced in ten 

 days ; on the eleventh day four 

 millions, and on the twelfth sixteen 

 millions. Ehrenberg has described 

 and figured more than 500 species 

 of animalcules; he has found 

 them in fog, in rain, and in 

 snow. 



I'NGTJINAL. (from inguen, Lat.) Per- 

 taining to the groin. 



INK-BAG. A bladder- shaped sac found 

 in some species of cephalopods, 

 containing a black and viscid fluid, 

 resembling ink, by ejecting which, 

 in case of danger from enemies, 

 they are enabled to render the sur- 

 rounding water opaque, and thus 

 to conceal themselves. Examples 

 of this contrivance may be seen in 

 the Sepia vulgaris and Loligo of 

 our seas. To the late Miss Mary 

 Anning we owe the discovery of 

 numerous fossil ink-bags, found in 

 the lias of Lyme Regis, still dis- 

 tended, as when they formed parts 

 of the living animals. The contents 

 of the ink-bags of cephalopods is 

 used in drawing, the sort preferred 

 is from an oriental species of sepia; 

 some of that extracted from a fossil 

 ink-bag found in the lias was used 

 by Sir Francis Chrantrey, on the 

 request of Dean Buckland, and was 

 by a celebrated painter, who was 

 ignorant of the particulars, pro- 

 nounced to be sepia of excellent 

 quality. This extreme indestruct- 

 ibleness of sepia arises from its 

 being chiefly composed of carbon. 



INOCERA'MUS. A genus of fossil bi- 

 valvular shells of great range, ac- 

 cording to some authors, extending 

 from the Silurian to the chalk, 

 inclusive. Pictet refers the Ino- 

 ceramus of the Silurian and De- 

 vonian periods to Posidonomya. 



INOSCULATION. "Dm n ^J junction 

 of the extremities; the union, or 

 junction, of the mouths of vessels, 

 as arteries with veins. 



I'NSECT. (insecta, Lat. insecte, Fr. 

 imitto, It.) The third class of 

 articulated animals provided with 

 articulated legs ; they possess a 

 dorsal vessel analogous to the ves- 

 tige of a heart, but are wholly 

 destitute of any branch for the 

 circulation. Insects breathe at- 

 mospheric air by means of tracheae, 

 which are most freely ramified 



