,8,=. RESEARCHES ON MOVEMENTS OF DIATOMS. 539 



molecular movements as soon as the granules are united with the 

 thread, and (3) from the circumstance that the end of the thread 

 sometimes winds itself up into a tangle. Moreover, the thread 

 not unfrequently appears interrupted for a stretch, owing to the 

 Indian ink granules being wanting for some cause on this portion of 

 it, it may be on account of less adhesiveness of the thread, or from 

 want of granules at the moment of its formation. Usually the thread 

 is long enough to project back beyond the diatom ; at times, however, 

 the formation was observed of unusually long threads, far exceeding 

 the whole length of the diatom. But after a time the threads break 

 off, together with the clumps formed by rolling up of their ends, and 

 then they remain still while the diatom continues to move forwards. 

 The formation of the thread proceeds by jerks, which harmonises with 

 the peculiar jerking movements of the diatom. 



Sometimes, instead of a thread on each side running backwards, 

 as when the diatom is gliding forwards, one thread runs backwards, 

 the other forwards, and the diatom revolves. In some instances it was 

 possible to follow the behaviour of the threads during a reversal of 

 movement. The threads carried at their extremities a clump of ink 

 granules. After the diatom had come to rest, it could be observed 

 that the clump was drawn back to the nodal point of the raphe, 

 apparently by shortening of the thread. In a short time a new 

 thread was developed, pushing out the clump of granules at its 

 extremity, but in the opposite direction to the former thread. The 

 diatom then began to move in a direction opposite to that it formerly 

 took. 



From these observations Professor Butschli draws the following 

 conclusions : — " It can hardly be doubted that the jerking elongation 

 of the threads stands in causal connection with the locomotion of the 

 diatom. Now, since it is known that diatoms, as a rule, only move 

 upon a solid surface, it would be an obvious assumption that the 

 threads fix themselves in some way upon the surface, and by their 

 elongation push the diatom forwards in jerks. On the other hand, 

 however, the rocket-like shooting out of the threads would be quite 

 sufficient, even without fixation of their ends, to explain, by means of 

 the resistance of the water, the jerking progress forwards of the 

 diatom. To me, indeed, the latter explanation appears to have more 

 in its favour, since we never could determine with certainty any 

 fixation of the threads to the underlying surface ; and the above 

 described tangle of their ends, and, further, the pulling back and 

 apparent drawing in of the thread during change in the direction of 

 the movement, speak against such a fixation. There would always 

 be a possibility that the peculiarity of our fresh-water diatoms, of 

 moving only upon a solid surface, is connected with the fact that 

 they cannot as a rule float. We should then have to refer the cause 

 of diatom movement to an abundant production of sticky jelly, which 

 shoots out quickly and with some force at the nodal points of the 



