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EHRENBERG, 1836. 17Notwithstanding the comparative imperfection of the optical appliancesat his disposal, itmay indeed with justice be said that Ehrenberg'sfigures, so far as they relate to contour and broad superficial details ofstructure, are scarcely to be improved upon, and considerably excel, inexecution, the delineation of the same forms included in many moremodern treatises. Ehrenberg, like Miiller, associated together under thecollective title of the Infusoria a vast assemblage of minute animal andvegetable organisms, a small section only of which finds its equivalent underthe same classificatory term in its more modern and restricted sense. Inaddition to the true Infusoria he still retained the Rotifera, or wheelanimalcules,the descriptions and illustrations of these monopolizing overone-third of the text and plates of his entire volume, while a very considerableportion of the remainder isoccupied with the description anddelineation of the essentially vegetable Desmidiaceae and Diatomaceae, towhich are also added many forms of Rhizopoda and unicellular plantsother than the Bacillaria.It was to the residual portion, that alone coincides with the tribeInfusoriaas at present recognized, that Ehrenberg attributed the possessionof a highly complex internal structure, whose chief feature was furtherdescribed as consisting of a large number of pedunculate bubble-likestomach-cavities associated with one another in a clustered form. The mostweighty testimony relied on by Ehrenberg in support of this theory wasderived from his repetition and extension of the experiments of Gleichen,by whom it was demonstrated that carmine, indigo, or other pigmentarymatter suspended in the water was freely devoured. After passing throughthe oral aperture this coloured matter was found to become collected insmall spherical bubble-like masses, variously distributed throughout thebody-substance or parenchyma, and without apparently taking the painsto assure himself that these vacuoles occupied a permanently fixedposition, Ehrenberg assumed that such was the case, and assigned toeach vacuole the significance of a distinct food-receptacle or stomach ;itwas with special reference to these supposed numerous stomach-cavitiesthat the title of the Polygastrica was adopted by him for the distinctionof this particular group. Ehrenberg's conception of the high andcomplex organization of his so-called Polygastrica, however, by no meansended here. The transparent vacuole possessing the property of contractingrhythmically, first observed by Spallanzani, conjointly with the still moreuniversally recognized gland-like nucleus or endoplast, were pronounced tobe integral parts of the male generative organs, the former representing aseminal vesicle, and the latter a seminal gland or testis. The minutegranular corpuscles distributed more or less abundantly throughout thesubstance of the body were declared to be eggs, which after fecundationfrom the seminal vesicle were discharged through the anal aperture orvent. The possession by these Polygastrica of a complex muscular,nervous, and blood-circulating system was likewise insisted on, though noC