206 THE AMERICAN MONTHLY [July, 



the presence of tlie phenomenon which I have described. 



As illustrating further some of the appearances, I ob- 

 served Navicula viridis travelling in a group of four 

 united frustules, convey simultaneously, three grains of 

 sand on three of the frustules, one apiece, in the same 

 direction, the three grains moving all in a line, and one 

 grain of sand moving in an opposite direction all at the 

 same time, three of the grains of sand being on top of 

 the frustules and the fourth, under the frustule of the 

 frustule that carried no grain on its upper surface. I 

 also observed a large active Nitzschia sigma, constantly 

 carrying grains of sand along both opposite margins, in- 

 differently, and the selfsame Nitzschia caught up and con- 

 veyed along one of its marginal edges, two grains of 

 sand which starting from the opposite ends met at the 

 middle portion of the Diatom, the frustule while thus en- 

 gaged, presenting its sigmoid outline. 



I also witnessed living Bacillaria paradoxa, having 

 two minute frustules of Gromphonema, attached by 

 stipes to their frustules, and projecting out at right an- 

 gles in a parasite-like manner, which rode backward and 

 forth with every retraction or extension of the line of 

 frustules, and whenever the Bacillarise forced their way 

 througli matted debris, the minute Gomphonemas were 

 bent back against the sides of the frustules bearing 

 them, until the debris was passed, when they would 

 stand out as before, thus proving that the stipes were 

 firmly attached to the siliceous frustules bearing them, 

 and that the stipes were flexible and acted like springs, 

 and therefore limited strictly in their movements to the 

 movement of their host. 



I added lead pencil (graphite) parings to the water on 

 the slide, and observed many small Naviculse gathering 

 up and rapidly circulating upon their frustules the par- 

 ticles of plumbago, constantly exchanging one particle 

 for a new particle (this I did in lieu of any indigo). At 



