The Cilium. 183 



strafed, we may assume that these structures are real. It is from this 

 point of view that the present investigation is pursued. 



Finer Structure of Cilia. 

 - ''Ueber den feineren Ban aller genannten Organellcn sind die 

 Angaben iiberaus sparlich, die meisten Beobachter sahen nichts als 

 hyalines Plasma" (Putter, 1903, p. 15). This is a fair statement of 

 recent views. Although a study of ciliary action has led to certain 

 fairly well-founded conclusions as to their probable structure, few 

 direct observations of their finer anatomy have been made. 



Englemann (1881, p. 511) points out that all large cilia, ciliary 

 membranes, etc., are made up of fine fibrils. These fibrils corre- 

 spond to those of all contractile structures. 



Kliennenberg (1886) took the ground that the large "Geiseln der 

 Wimperringe (bei Lopadorhynchus, Polycha) aus 20 bis 30 Cilien 

 bestehen" (Putter). 



Jensen (1887) figures, for the tail of sperms, fibrils that were 

 brought out by pressure on the cover glass. Judging from his draw- 

 ings the fibrillar structure is very evident. 



Ballowitz (1886 and later), in a series of contributions to the 

 structure of spermatozoa, gives some strong evidence for fibrillar 

 structure in these organoids. In another paper (1890) he holds 

 that contractile tissues, wherever found, are fibrillar. There is no 

 doubt from his drawings that this is true, at least in the sperms. 



Schuberg (1891) describes the "Zusammensetzung der Membranel- 

 len" of Stentor coeruleus and bursaria and of some hypotrichous infu- 

 sorias. They consist, according to him, of two ''Reihen" of fibrils. 



Stevens (1901) asserts that the aboral membrane of Licnophora 

 macfarlandii, Stevens, consists of fine long cilia, which are visible in 

 the living animal under high magnification. (Putter.) 



Theories of the Structure of Cilia. 



Although there are a few direct observations on the finer anatomy 

 of cilia, a number of theories of their probable structure have been 

 advanced. These are admirably summed up by Putter, pages 27-29. 



They are, in l)rief : First, that the cilia are lifeless processes at- 

 tached to the cell. They are somewhat stiff and are moved by active 



