The Cilium. . 191 



strated to consist of four fibrills which had a spiral arrangement. 

 (Fig. 4 and 5.) They were not traced into the cell and their rela- 

 tion to the cell body was not determined. 



Spirillum. 

 With flagella of bacteria we descend the scale to still more minute 

 forms which are not visible by ordinary histological methods. Still, 

 no question can exist as to their active contractions. Thus, in any 

 tissue cell there may be contractile elements or fibrillae which are 

 invisible by ordinary methods. If simple, single-fibril, cilia or 

 flagella exist, we should expect to find them among these most minute 

 organs of bacteria. It is j)roposed to devote a special research to this 

 point. At present I am able to ofi^er the evidence from a single type. 

 A large Spirillum common in stagnant water when stained by Loef- 

 fler's method shows unmistakably that its long, apparently simple 

 flagellum consists again of four spirally-wound fibrillae. "While not 

 demonstrated alive by the teasing method used for Euglena and 

 chilomonas, it is not difficult to find among the stained specimens a 

 complete series from the apparently solid, simple flagellum through 

 all stages of uncoiling to four distinct fibrillae. (PI. IV, Fig. 8 and 

 Text Fig. 5a.) 



Theoretical Considerations. 



As mentioned above. Putter (1903), after a discussion of the 

 fibrillar theory of the structure of cilia, rejected it because of the 

 difiiculties met with in applying it to the movements of the flagellum. 

 Parker (1905), in a discussion of the probable structure of cilia, does 

 not agree with Putter and prophesies that even flagella may be fibril- 

 lar. From the above observations it is evident that this is true, at 

 least, for three flagella. In these observations Putter's objections to 

 the fibrillar theory become groundless, and the scant attention paid 

 Schafer's tube theory of ciliary structure is also justified. 



Although only three have been demonstrated to be fibrillar, these 

 make it probable that all flagella have a similar structure. The work 

 on cilia to follow proves that they are constructed on the same gen- 

 eral plan, though diiferent cilia vary in the number of their compo- 

 nent fibrillae. 



