INFUSORIA

(Lat. infundo, //)o«rm.) A name applied by Otho Fr. Miiller to an a emblage of microscopic animalcules which are for the most part developed in infusions of decayed animal and vegetable substances. Some of these minute organized beings were known to Linnaeus, and were placed by him at the end of the cla Vermes, in a genus which he denominated Chaos. Miiller, who made the Infusoria a subject of special study, discovered numerous distinct genera and species, which he named and cla ified according to their outward form. Gmelin and Lamarck introduced Miiller's discoveries and cla ification of the Infusoria into their systems without any particular modification. Cuvier, in 1829, observes, that " Naturalists usually close the catalogue of the animal kingdom with beings so extremely minute as to be invisible to the naked eye, and which have been discovered only since the invention of the microscope has unveiled to us, as it were, a new world. Most of them present a gelatinous body of the greatest simplicity, and for these this is undoubtedly the situation; but authors have placed among the Infusoria animals apparently much more complicated, and which only resemble them in their minutene and the dwelling in which they are usually found." These higher-organized Infusoria were placed by Cuvier at the head of the cla in a distinct order, under the name of Rotiferes or Rotifer a, a name which has subsequently been retained. Cuvier attributes to these animalcules a mouth, a stomach, an intestine, and an anus; and notices the prominences on the anterior part of the body, which some observers had regarded as e^es. The anterior lobated organ and its vibratory denticulations, the succe ive action of which gives to the organ the appearance of a swiftly rotating wheel, forms the main external character of the order. Cuvier includes in the order Rotator i a the genera Furcular i a, Lam.; Vagi nicol a, Lam.; Tubicolar i a, Lam.; Brach i on us, Miiller. The investigations of Ehrenberg, with the aid of a superior microscope to that of his predece ors, have brought to light many additional organs and complexities of structure in the Rotifer a, besides several genera and species before unknown; and since these researches naturalists have generally regarded the Rotifer a as a distinct cla of Invertebrata, which Profe or Grant has placed in the Articulate sub-kingdom, and Profe or Owen in the Nema ton eur a, or higher division of Cuvier's Radiata. For the character, subdivision, and organization of the Rotifer a, see that word. The second order of Infusoria in Cuvier's system is denominated Homo gene a; a term sufficiently expre ive of the inadequate ideas current at that recent period respecting their organization. Cuvier says, " The body of the Homo gene a presents neither viscera nor other complication, and is frequently destitute of even the appearance of a mouth." Ehrenberg has since shown that tliey have not only really a mouth, but that the greater part INITIATIVE. of the Homo gene a of Cuvier po e a digestive cavity complicated with many caecal pouches or stomachs; and accordingly proposes to name the order Poly gastric a. Cuvier Includes in his second order of Infusoria the genera Urceolaria, Lam.; Trichoda, Leucophra, Kerona, Him an top us, Cercaria, Furcocerca, Vibrio, Proteus, Volvox, and Monas. As the poly gastric structure has not been detected in any species of Cercaria, but as, on the contrary, some species, as Cercaria lemrue, po e a simple alimentary canal, this genus, together with the cercarial Spermatozoa, and the Vibrionidce, which all po e a straight and simple alimentary canal, have been removed from the Infusoria, and cla ed by Mr. Owen with the Entozoa. Thus the animals of infusions, although of comparatively simple organization, po e ing neither a heart nor respiratory organs, yet manifest at least three distinct types of structure, and are referable to three different cla es of animals. Many genera of Infusoria are protected by an external siliceous case. The observations which Ehrenberg had made on the modifications of the form and surface of these cases of the existing Infusoria led to his capital discovery of their remains in a fo ilized state. The mineral called Polir-scheifer, used for a long period in the arts for polishing metals and other substances, was first dicovered to be composed of myriads of the microscopic flinty cases of poly gastric Infusoria belonging to the genera GrilioncUa, Bacillar i a, Diatorna, . Whole strata of considerable extent and thickne have since been found to consist almost exclusively of the fo il remains of Infusoria. [s. 612]