1865.] Kolliker's Outlines of the Lowest Forms of Life. 533 



been to a great extent defined, and systematic zoologists have been able, 

 in some degree, to arrange and classify them in the various groups 

 to which they belong. As to the phases through which the history of 

 the true Infusoria has passed, these are easily summed up. Ehren- 

 berg considered (and we believe still considers) them to be microsco- 

 pical aniinalcuhe of comparatively high organization ; and the error 

 he committed was to seek and imagine that he had found in them a 

 structure identical with that of the higher animals. That they are 

 to a certain extent so endowed is quite true, but whilst he over- 

 looked or failed to trace the homologous features which actually exist, 

 he invested them with others which they do not possess, and wherein 

 they are in reality rather allied to plants than to animals. Thus he 

 ascribed to them a mouth, throat, numerous true stomachs in which he 

 and his disciple Pouchet professed to see distinct membranes (hence 

 Ehrenberg's term Polygastrica), and a connecting intestinal canal ; 

 also a heart, true circulation, and a " nucleus ' : or germ, with a " nu- 

 cleolus " or germinal vesicle. Their method of reproduction he be- 

 lieved to be similar to that of plants, by subdivision, and gemmee or 

 buds. It may be briefly stated that although he was to a certain extent 

 correct in his observations concerning the multiplication of these 

 forms, yet, as will be shown presently, it is precisely here that they 

 are most closely linked to the animal kingdom, whilst his imaginary 

 stomachs ally them rather to some of the lowest forms of plant life. 



In the course of time, and after a somewhat acrimonious contest, 

 the opponents of Ehrenberg succeeded in sweeping away his whole 

 anatomical system, and Dujardin degraded the infusoria to the 

 position of unicellular animalcule, formed of a substance which he 

 called " sarcode," almost void of organic structure, but possessing the 

 power to ingest food through an oral aperture, that food collecting in 

 "vacuoles," or improvised globules (the stomachs of Ehrenberg), 

 and rotating in or with the sarcode, somewhat after the manner of 

 the semi -gelatinous " protoplasm " in certain lowly algse. Other 

 observers compared the " heart " or " contractile vesicle " to the 

 "vascular water system" of certain "vermes," and the "blood" 

 was believed to be a liquid admitted from without, rather than a true 

 circulating fluid, the result of digestion. Thus, if we may be per- 

 mitted to indulge in a passing joke, the poor little infusoria were 

 made to look smaller than they really are ; but they were reserved for 

 a higher destiny, chiefly in consequence of the able researches of Dr. 

 Balbiani of Paris, to whom reference has often been made in these 

 pages ; it will be found from the work under review, although they are 

 placed by the author below three other groups of Protozoa, that they 

 are really possessed of a tolerably well- developed animal organization. 



The " polygastric " system of Ehrenberg has, it is true, disap- 

 peared for ever, and the alimentary apparatus consists of an oral aper- 

 ture or mouth, a gullet, which the author believes to be in all cases 

 contractile, temporary digestive vesicles which rotate within the uni- 

 cellular animalcule, a contractile vesicle of the nature of a heart ; a 

 circulating system of minor vesicles, an anal aperture for the discharge 

 of exhausted alimentary substances. Of the " circulating apparatus," 



