THE MECHANISM OF DIATOM MOTION. 



BY T. CHALKLEY PALMER. 



Previous papers in these Proceedings have dealt with 

 the general nature of diatom motion, and the endeavor has 

 been to present clearly the reasons for thinking that the phe- 

 nomenon is an outcome of protoplasmic work, and in no 

 degree explicable on any " theory of osmosis." For the rest, 

 it remains to learn if possible the mechanism by means of 

 which the protoplasm acts upon its surroundings to push the 

 diatom along. Protozoa and the spores of algse swim through 

 the water with the aid of obvious cilia and flagellae. Rhizo- 

 pods crawl along solid surfaces by alternately expanding and 

 contracting portions of their naked sarcode in different direc- 

 tions, so showing the phenomena of the pseudopodia. These 

 things are easily observed, but the locomotion of the diatom 

 is another matter. Immersed in its native element, and in 

 the full enjoyment of health, the living substance, enclosed 

 in a beautiful box of opal, ordinarily reveals under the best 

 lenses no external organs whatever. Yet, as we have seen, 

 the motion is often of a stubborn and strenuous nature. 

 Mechanism of some sort there must be. 



First of all, it is to be said that both vibrating cilia and 

 pseudopodia have been alleged in certain cases. But it is 

 now universally agreed that the observations leading to the 

 notion of cilia (where there were any real observations) are 

 one and all capable of other interpretations, and that the 

 deductions in this direction are due to a misconception of 

 fairly elementary facts. According to a wide concensus of 

 opinion, cilia do not exist among diatoms; and in case of 

 many of the larger motile .species, it is impossible to see how 

 typical cilia could exist. As to pseudopodia, the matter is 

 not quite capable of such crisp statement. But it may still 

 be said with rigor, that visible pseudopodia, liice those of the 

 rhizopods, have not been seen operating in the living antl 

 moving diatom. 



