F. DU7ARDIN, 1841. T. VON STEBOLD, 1845. 1 9 



consistence, although, through the superaddition of a denser external 

 membrane, they were incapable of emitting thread- or root-like pseudo- 

 podic processes. No trace of a muscular or nervous system could be 

 detected by this authority, while the non-existence of the complex digestive 

 apparatus described by Ehrenberg was effectually demonstrated. On 

 feeding Vorticellae and other animalcules with carmine, in accordance with 

 the plan adopted by Gleichen and Ehrenberg, Dujardin found that the 

 food-particles, after their reception at the oral aperture, were not retained 

 in definite and permanently fixed stomach-sacculi, but after aggregation 

 into small spheroidal masses were passed backwards into the body-sarcode 

 or parenchyma, and there freely circulated until digestion or rejection at 

 the anal aperture. The somewhat similar and characteristic independent 

 circulation of the inner sarcode or parenchyma of Paramecmm bursaria 

 and Vaginicola crystallina was also recorded for the first time by Dujardin. 

 The contractile organ, first discovered by Spallanzani, and interpreted by 

 Ehrenberg as belonging to the reproductive system, was pronounced by 

 this investigator to be a mere vacuolar space situated close to the surface, 

 apparently fulfilling a respiratory function by the continual absorption and 

 expulsion of water. 



This simple interpretation of the organization of the Infusoria arrived 

 at by Dujardin, in opposition to that of Ehrenberg, soon gained powerful 

 adherents. Among the more noteworthy authorities who also by their 

 independent and almost contemporaneous researches, arrived at conclusions 

 coinciding with those of Dujardin and antagonistic to the polygastric 

 theory, may be mentioned the names of Meyen and Focke. Thuret and 

 Unger, again, from a botanical point of view, indicated the close correspon- 

 dence of the zoospores of Chara, Vaticheria, and various confervoid algae 

 with the monadiform animalcules referred by Ehrenberg to the genera 

 Chlamydoinonas, Phacelonionas, and Microglena. The most decisive advance 

 made towards the elucidation of the true structure and affinities of the In- 

 fusoria, following upon Dujardin's investigations, was, however, accomplished 

 by Carl Theodor von Siebold. It was this biologist who, in his ' Text-book 

 of Comparative Anatomy,' published in the year 1845, first enunciated the 

 theory, anticipated to some extent by Oken, Schleiden and Schwann, 

 that the representatives of the Infusoria were unicellular organisms. Each 

 separate animalcule possessed, in his opinion, the value only of a simple 

 cell, of which the central gland-like organ observed by so many previous 

 authorities, was now for the first time declared to be homologous with an 

 ordinary cell-nucleus, and described under a like distinctive title. The 

 contractile spaces or vesicles were further interpreted by Siebold as possess- 

 ing a circulatory or cardiac function. The simple sarcodic nature of the body- 

 substance of the Infusoria, first pointed out by Dujardin, was fully recog- 

 nized by this authority, and all the organisms possessing such a simple 

 unicellular structure were assembled together as the representatives of 

 an independent sub-kingdom of the Invertebrata, upon which he conferred 



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