1893.] NEW-YORK MICROSCOPICAL SOCIETY. 97 



outer frustules must certainly operate inversely to each other, 

 or are not, at least, synchronous and impulsing in the same 

 direction. This is merely suggested as an hypothesis of cause of 

 motion. 



As expanding further the subject of motion in the diatom, I 

 will offer another phase that may have a useful bearing on cer- 

 tain of such hypotheses long in print and subject to revision. At 

 another tifne, while seeking clues to the presence of the proto- 

 plasmic covering, I followed a large Navicida viridis in its move- 

 ments through the water, as seen in the field of the microscope, 

 the slide being uncovered. In the wake of the retreating end of 

 the diatom there appeared to be a form of attractive suction over 

 minute particles along its line of transit. A train of minute par- 

 ticles lagged along after the passage of the diatom, at a distance 

 to the rear of about the width of the diatom, until the attracting 

 power had ceased to act, when they would become still. The 

 particles vvere drawn in semicircular arcs from either side of the 

 axial line of the diatom's passing range, the axial line being tan- 

 gential to the opposing arcs of motion of the particles following 

 in the wake of the diatom. It would have been impossible for 

 this movement of particles to have taken place if the motion of 

 the diatom was caused by the expulsion, at any time, of infini- 

 tesimal jets of water. Likewise it offers an insuperable objection 

 to the theory of motion accredited to Prof. Hamilton L. Smith 

 and quoted from Wolle's " Diatomacese of North America " : 

 '^that the motion of the Naviculae is due to injection and expul- 

 sion of water, and that those currents are caused by different ten- 

 sion of the membranous sac in the two halves of the frustule," 

 etc. Wolle also quotes Cornelius Onderdonk as ascribing the 

 movements of diatoms to "a thin fluid mass in rhythmical mo- 

 tion," which Onderdonk had elsewhere proved to his own mind 

 by experimental dyeing tests : " The fluid rhythmical mass cov- 

 ered the surface of the diatoms.'' I looked up the original com- 

 munication of Onderdonk and read it. While his experiments 

 were very interesting, he had made no reference whatever to the 

 power of the protoplasmic layer to capture and tenaciously hold 

 and transport, at its own volition, appreciable masses of living 

 particles. 



It may not be inappropriate to introduce herein a transcript of 



