98 JOURNAL OF THE [October, 



Rev. W. Smith's views in regard to the motion of diatoms, quoted 

 in Carpenter, edition of 1856: "Among the hundreds of spe- 

 cies which I have examined in every stage of growth and phase of 

 movement, aided by glasses which have never been surpassed for 

 clearness and definition, I have never been able to detect any 

 semblance of a motile organ, nor have I, by coloring the fluid by 

 carmine or indigo, been able to detect in the colored particles sur- 

 rounding the diatom those rotary movements which indicate in 

 the various species of animalcules the presence of cilia " ('' Syn- 

 opsis of British Diatomaceae," Introduction, p. xxiv.). This quo- 

 tation would also seem to indicate that the Rev. W. Smith was 

 not acquainted with the peripheral motion of the protoplasmic 

 \z.y^x oi Amphiprora, for if he had been acquainted with this he 

 would have had to modify the above opinion and substitute a 

 form of motility independent of any easily seen ciliary processes. 



The theory which the sum total of my experience so far sug- 

 gests is that the motion is probably caused by an infinitely rapid 

 undulatory motion of the protoplasmic sheath, which I assume to 

 exist, covering the diatom on all sides, which vibratory pulsations 

 are too minute to be seen under any degree of magnification, and 

 whose reactionary beats against the water cause the forward or 

 retrograde movements at the instinctive will of the diatom. 



Returning to the theory of propulsion advanced by Prof. H. L. 

 Smith, and with all due regard for his long and signal experi- 

 ence in the study of living and other diatoms, I would respect- 

 fully call attention to some points calculated to weaken, or even 

 vitiate, the claims of any expulsive action connected with a me- 

 dian diaphragm separating any two frustules that are united and 

 in motion. The quadruple frustules are fairly quick in their pro- 

 gression. Were the hypothesis actually true for a single indi- 

 vidual, we would, in the quadruple instance, have four frustules 

 propelled by tv/o exterior sides, and eight opposing prows, leaving 

 the three central enclosed walls in "innocuous desuetude" until 

 each frustule was allowed to shift for itself. 



Before finally disposing of the question of motion of diatoms, 

 I would like to advance two more points of interest bearing 

 strongly upon the subject. In the brackish material containing 

 Amphiprora ornata there were numerous specimens of Nuviciila 

 Smithii. I gave some attention to one of these, and if the rela- 



