LINNEAN SOCIETY OF LONDON. XI 



It is scarcely necessary to remind you that the first important 

 advance which, during the present century, was made in our know- 

 ledge of the Infusoria dates from the publication of the great work 

 of Ehrenberg *, whose unrivalled industry opened up a new field of 

 research when, by his expressive figures and well-constructed dia- 

 gnoses, he made us acquainted with the external forms of whole 

 hosts of microscopic organisms of which we had been hitherto en- 

 tirely ignorant, or which were known only by such figures and de- 

 scriptions as the earlier observers with their very imperfect micro- 

 scopes were able to give us. 



Ehrenberg, however, as we are all aware, did not content himself 

 with portraying the external forms of the microscopic organisms to 

 whose study he had devoted himself, but sought also to determine 

 their internal structure, of which scarcely any thing had been hitherto 

 known. In this direction, no less than in the other, the perse- 

 verance of the celebrated microscopist never flagged ; but unfortu- 

 nately at the very commencement of his researches he slid into a 

 misleading path, and was never again able to find the right one. 



Every one knows how Ehrenberg, in accordance with preconceived 

 notions of the high organization of all animals, attributed to the Infu- 

 soria a complicated structure ; how, while he rightly distinguished them 

 from the Rotiferae, with which they had been confounded by 

 previous observers, he yet regarded them as intimately related to 

 these representatives of a totally different type ; and how, in attri- 

 buting to them a complete alimentary canal with numerous gastric 

 offsets, he took this feature as their most important character, and 

 designated them by the name of Polygastrica ; and it is probably 

 a matter of surprise to many of us that with the overwhelming mass 

 of evidence which subsequent research has brought to bear against 

 the truth of the polygastric theory, the great Prussian observer 

 should still adhere with undiminished tenacity to his original views. 

 Among the authors who, since the publication of the *Iufu- 

 sionsthierchen,' have contributed most to a correct estimate of the 

 morphology, physiology, and systematic position of the Infusoria, the 

 names of Dujardin, Von Siebold, Stein, Balbiani, Claparede and Lach- 

 mann, and most recently Haeckel stand out conspicuous. 



The way to a philosophic conception of the Infusoria and of other 



beings which occupy the lowest stages of life was undoubtedly 



opened up by Dujardin f when he drew attention to a peculiar form 



* Die Infusionsthierchen als vollkommene Organismen. Leipzig, 1838. 



t " Sur rOi'ganisation des Tufiisoires," Ann. des Sci. Nat. 1838 ; and ' Hist. 



des Infusoires,' Parif. 1841. 



