196 THE AMERICAN MONTHLY [July, 



many ciliated infusoriaus he partly suggested that the 

 phenomenon reminded him of the well-known hy- 

 draulic experiment of causing a cork ring or ball to be 

 revolved by the contact of a jet of water, or in his own 

 language "of the rotation of the little balls of indigo, 

 which is the most curious part of these observations 

 there can be no doubt, and we may well ask, how is it 

 to be explained ? One can very readily fancy a minute 

 jet of fluid, issuing from the interior of the frustule 

 through the little opening, or dot, and thus causing this 

 rotation ; it is not unlike the well-known hydraulic ex- 

 periment, which I have frequently exhibited of a cork 

 ring clinging to the side of a jet of water and rotating ; 

 but if this be so where is the water entering the frus- 

 tule to keep up the supply ?" 



While, after sufficient as well as attentive watching, I 

 did not observe any particular motion of granules, bacte- 

 ria or other matter moving in the liquid in the vicinage 

 of the nodular areas, I did frequently see minute parti- 

 cles, such as bacteria transported by the movement of the 

 exoplasmic sheath to where the nodular depressions 

 occur, and they were then lost to view. (Not having any 

 indigo pigment convenient at the time, I could not make 

 the test by that medium of the formation of the little 

 balls, but trusted more particularly to the minute infuso- 

 ria, bacteria and other particles already in the liquid). 



But while seeking for these effects, I incidentally ob- 

 served that active monad infusoria were very readily 

 entrapped by the exoplasm of the diatoms ; as I watched 

 several thus caught, for a reasonable time, and I noted 

 that they struggled with an incessant pendulum-like vi- 

 bration to free themselves, but. without avail. It is readily 

 seen that failing to release themselves, they would finally 

 cease to struggle and would settle down on the diatom, 

 where it would probably be absorbed or assimilated by 

 the protoplasmic covering of the diatom. Professor 



