Edwards.J 212 [February 9, 



species appearing both in the free and attached conditions, and this 

 is even more strikingly illustrated in Schizonema. 



Bacillaria paradoxa is usually set down as the most rapid in motion 

 of the Diatomacese, its velocity being recorded by Smith, as he meas- 

 ured it, at over one two hundredth of an inch in a second. This is 

 certainly pretty quick when we consider that the length of the frus- 

 tule is only .0025 of an inch. But my experience has been that its 

 velocity varies in every degree from that mentioned to perfect rest; 

 at times some individuals will be in rapid movement, while others are 

 motionless; and also I have remarked that from sunrise to noon seems 

 to be the period during which, under ordinary conditions, the move- 

 ment is most active, while during the afternoon it is very sluggish, 

 and at night almost nil. This Amphora, as I saw it at the time 

 mentioned, was moving even more rapidly than I ever saw a Bacillaria 

 move, and that with a steady onward progression very different from 

 that of most naviculiform diatoms. 



It appears to me that in Schizonema and similar genera, which 

 consist of siliceous loricated naviculiform frustules enclosed in mem- 

 branous tubes, as soon as a rupture of the investing membrane takes 

 place, by fracture or tearing asunder, almost immediately a knowl- 

 edge of the fact is in some way communicated from the point at which 

 the opening occurs to all other points of the tube, as at once the con- 

 tained frustules which hitherto have been at perfect rest or, at most, 

 only moving to a very slight extent, and even then in an extremely 

 sluggish manner, become animated in their motion, and the most of 

 them move towards, and attempt to escape from, the opening made. 

 And this evidently does not result, as might at first have been sup- 

 posed, from any pressure exerted upon them from the closed end of 

 the tube, and which, therefore, only shows itself when the obstacle 

 in the shape of the investing membrane is suddenly removed. For 

 the motion is the true lively action peculiar to the living individual 

 in the naviculiform Diatomacese, and is not in all cases towards the 

 opening made, but often many, or, as in some cases which have come 

 under my observation, most of the frustules begin to move in an 

 opposite direction at first, while at the same time many escape by the 

 opening in the tube, and thereafter assume vigorous motion in the 

 surrounding liquid. Again, usually some of the frustules being, as at 

 first appears, carried along by the stream constituting the mass of 

 those moving towards the opening, all of a sudden seem to change 

 their minds, or are struck with an idea, if I may so express myself, 



