1889.] MICROSCOPICAL JOURNAL. 81 



Motions of Certain Diatoms and Oscillaria. 



By WM. a. terry, 



BRISTOL, CONN. 



In a previous article published in this periodical I stated that vigorous 

 specimens of certain diatoms would travel a distance equal to their 

 length in about tvvo seconds ; this is maximum speed, and is not 

 common except in small forms, the average rate being about five seconds. 

 The Pleurosigma^ although as active as most varieties, requires about 

 seven seconds to travel its length, as it is much longer than most other 

 kinds. 



I sometimes see published statements from other observers that are 

 not in accordance with my observations. One writer states that diatoms 

 always travel with one valve uppermost ; others sav that the valves are 

 in a vertical position, showing the hoop. Staiirotteis acuta travels 

 with the valves vertical, showing the broad hoop or band and the edges 

 of the valves or shells. So, also, do several varieties of Phinularia 

 and Siirirella. Stauroneis phenicenteron ti'avels with the shells hor- 

 izontal, showing one uppermost ; as also several Pinmdaria^ Stirirella^ 

 etc., including all the Plejirosigma. In studying the motions of such 

 diatoms as the Pleui-osigjua from Dike creek, it is difficult to avoid 

 crediting them with .some amount of volition. Although blindly 

 running against obstructions without attempting to avoid them, yet 

 when stopped by such obstructions, the impulse is not continued in 

 that direction! as long as would be the case were the organism free 

 to move. It soon backs out and travels in the opposite direction. \\'hen 

 stopped bv an obstruction this diatom comes nearer to showing currents 

 in the water than any other I have observed, small particles passing 

 rapidlv along its side apparently without being in contact with it. Pieces 

 of sediment resting upon it near the median line may sometimes be seen 

 moving in an opposite direction to those in contact with the side. 



This uniformity of position in all the different individuals of the same 

 varietv during motion seems to me very suggestive, as indicating a line 

 of investigation by which their means of motion may be detected, and 

 also showing that their motions are not so purelv automatic as is gen- 

 erallv supposed. 



The motions of the Oscillaria seem to me to require a different ex- 

 planation from those usually given. Air. Wolle, in his ' Fresh-water 

 Algas of the United States,' quotes Dr. Hansgirg as advancing the sup- 

 position that the movements are of the same nature as those of the 

 sarcode in the pseudopodia of rhizopods. As the protoplasm is enclosed 

 in a rigid sheath, it is ditiicult to see how its movements can cause the 

 motion of the entire filament, as Dr. Hansgirg states it does not pro- 

 trude. Mr. Wolle believes the motion to be caused by the rapid di- 

 vision of cells. If an active filament short enough to be entirely within 

 the field of the microscope be carefully observed, it will be seen that 

 the entire filament is in uniform motion in the direction of its length, 

 and if the variety is one in which the ends are bent or curved it will 

 also be seen that the onward movement is accompanied bv a revolution 

 upon its axis, so that a point on the outside of the sheath describes a 

 spiral path through the water. After the filament has travelled a cer- 

 tain time in one direction, the motion stops and is then reversed. The 

 filament retraces its path in the opposite direction, the axial revolution 



