184 O. P. Delliiigcr. 



elements in the cell body. That is, tliey arc ''Beweg'bar, niclit bevveg- 

 lieli." This was the conception of the earliest observers and has 

 been recently revived by Benda (1891). Althongh it has at all times 

 had occasional supporters, Stuarf^ (1867), Xiissbamn (1877), Cla- 

 paredes (1875) and Kraft (1890), it has not, as a rule, appealed to 

 investigators. 



Second, that cilia are hollow elastic sheaths into which a fluid is 

 injected and withdrawn. This is the hypothesis advanced by 

 Schafer in 1891 and supported by him recently against an attack by 

 Putter. So far as I know, it has found practically no support among 

 investigators, most of them agreeing with Parker that there is little 

 in recent work to justify it. In fact, the continued activity of cilia 

 after complete isolation indicates that they contain within them- 

 selves their own. contractile material. 



Third, that cilia are complex fluids. This is the view of Verworn 

 (1890 and later), also of Jensen. This conception has been criti- 

 cized, Schenke (1890), in which criticism he gives the reasons why 

 contractile substance cannot be fluid. So far as cilia are con- 

 cerned, Reinke jDossibly expressed the objections to this view best 

 when he said : "Als fliissig oder halbfliissig konnen diese Geisseln un- 

 moglich gelten. Sie wiiren dann so wenig imstande, die mechanische 

 Arbeit der Portbewegimg der Spore zu leisten wie est moglich ist, ein 

 Boot zu bewegen mit Rudern die aus einer Fliissigkeit bcstehen." 



Fourth, that cilia hav^e a fibrillar structure and that the movements 

 are due to the contraction of these fibrils. The fibrils may be only 

 temporary arrangements of the molecules of an otherwise homogene- 

 ous substance. This is Putter's view. He thinks himself forced to 

 it by lack of structure in the flagellum. T do not think his position is 

 well taken, and if, as will be shown later in this paper, the flagella 

 are really fibrillar, he has no ground for it whatever. , 



Tn Engiemann's theory, first advocated by him in 1868 and devel- 



"Stuart bases bis view on observations made on ciliated cells of "Aoliden- 

 larven." He saw running tbi-ough the cells parallel fibers some of which 

 went to the nucleus. During cell activity, he observed that when the 

 cilia were in motion the nucleus was also affected, and concluded that the 

 structures in question were contractile fibers by which the cilia and nucleus 

 were moved. 



