5o ORGANIZATION OF THE INFUSORIA. 



whole, as indicated in the diagrammatic plan and tabular view given in the 

 preceding chapter. In order to meet present requirements, it has been 

 found desirable, nevertheless, to institute the following definition of the 

 Infusoria ; this, while according as far as possible with the broader prin- 

 ciples of the above-named scheme, includes all, and those only, of the 

 numerous and exceedingly diverse forms described in this volume. 



DEFINITION OF THE LEGION INFUSORIA. 



Protozoa furnished in their, adult condition with prehensile or locomotive appen- 

 dages, that take the form of cilia, flagella, or of adhesive or suctorial tentacula, but 

 not of simple pseudopodia; zooids essentially unicellular, free-swimming or sedentary ; 

 naked, encuirassed, loricate, or inhabiting a simple mucilaginous matrix ; single, or 

 united in colonial aggregations, in which the individual units are distinctly recog- 

 nizable ; not united and forming a single gelatinous plasmodium, as in the Myce- 

 tozoa, nor immersed within and lining the internal cavities of a complex proto- 

 plasmic and mostly spiculiferous or other skeleton-forming cytoblastema, as in the 

 Spongida. Food-substances incepted by a single distinct oral aperture, by several 

 distinct apertures, through a limited terminal region, or through the entire area of 

 the general surface of the body. Increasing by simple longitudinal or transverse 

 fission, by external or internal gemmation, or by division — preceded mostly by the 

 assumption of a quiescent or encysted state — into a greater or less number of sporular 

 bodies. Sexual elements, as represented by true ova or spermatozoa, entirely absent, 

 but two or more zooids frequently coalescing as an antecedent process to the 

 phenomena of spore-formation. 



The annexed plan of the further subdivision of the Infusoria into its 

 component sections, classes, and orders is necessarily an abbreviation only 

 of the tabular view of the Protozoa given at page 36, supplemented in the 

 present instance, however, with a brief summary of the more essential 

 diagnostic characters. 



The general Morphology, Organography, ^Etiology, Distribution, Repro- 

 ductive Phenomena, and all other features associated with the group of the 

 Infusoria as here defined may now be examined in detail, and under their 

 respective headings. 



Morphology. 



Unicellular Nature of the Infusoria. 



As implied in the definitions of the Protozoic sub-kingdom generally, 

 and of the Infusorial legion in particular, already submitted, any repre- 

 sentative zooid or individual unit of the group now under consideration 

 possesses according to the views supported by the author the morphological 

 value only of a simple cell. This interpretation, originating in its substantial 

 form with Carl Theodor von Siebold in the year 1845, was beyond doubt 

 foreshadowed many years previously by Lorenz Oken, received further 

 amplification at the hands of Schleiden and Schwann, and represents at the 

 present date the most generally accepted estimate of the organization of 

 the members of this class. From a very early period up to the present 

 time, however, there have not been wanting authorities of more or less 

 considerable eminence who have advocated on behalf of the Infusoria a 



