202 THE AMERICAN MONTHLY [July, 



both ala3 and without apparent intermission until it took 

 a retrograde movement, and backed away to a clear 

 water space. While observing this behavior in one of 

 the frustules, I also noticed that at one moment the 

 Surirella turned upwards in the field, axially, to the tube 

 of the microscope ; and for the first time, I was enabled 

 to understand the relation of the alse to the sides of the 

 frustule. If we conceive diagonals cut through a square, 

 and projecting some little distance beyond the corners, 

 we will then have a correct idea of their position with 

 reference to the frustule, or in other words they flare out 

 at an angle of about forty-five degrees to the sutural 

 edges, or to the lined valves. I also noted clearly that 

 in all four frustules, as examined, numerous spherical 

 corpuscles were in active and constant motion. The first 

 idea suggested by these appearances was that the spher- 

 ical corpuscles moving within the endoplasm were 

 minute monad-like Infusoria ingested by the Diatoms in 

 their feeding, yet still retaining their motile power. 

 Although I was quite familiar with Prof. Smith's refer- 

 ences to these corpuscles, his paper did not prepare me 

 for this surprise and I trusted to a careful observation 

 for my own account, so that I watched them attentively 

 in order to determine the apparent law governing their 

 motions. 



Also, bearing in mind the conjecture of Cornelius On- 

 derdonk, that the life movements of the diatoms might 

 be caused by some impulse on the inside walls of the 

 cell, somewhat after the manner of the cyclosis seen in 

 the cell structure of various well known water plants and 

 Desmids ; I very soon saw that this hypothesis had no 

 value in the case of the Surirella studied by myself, as I 

 found that the motile spherules went indifferently in any 

 direction in the field of movement to which they were 

 limited, two or more might pass each other going in op- 

 posite directions, and that they constantly crossed over 



