252 ON THE STRUCTURE OF OSCILLATORIyE. 



forward motion is active and the recoil passive. To observe 

 this well, the very uppermost surface of the filaments ought 

 to be brought in focus, leaving the margins rather undefined, 

 bearing in mind that the filament is not a flat but a cylindrical 

 body. As to the cause of these motions, or the mechanism 

 by which they are effected, nothing positive is known ; Dr, 

 Kingsley has observed the whole surface of a large species to 

 be covered with cilia, moving in a circular wave round the 

 axis of the filament. (Mic. Journal, No. xi. p. 243.) It 

 would be of the greatest interest to have this observation con- 

 firmed, as the presence of cilia would in a very great measure 

 explain their motions. As a further reason for such con- 

 firmation, T would assign the fact of having discovered, as I 

 believe, in the new species just described, a locomotive appa- 

 ratus within the filament, independent of cilia. While 

 attentively examining the green thread running through the 

 middle of the filament, it suddenly vanished in one cell, and 

 appeared more prominent in the next to it, repeatedly altering 

 its position in different cells, now vanishing, now appearing 

 again, without any other perceptible motion than a gentle 

 tremor of the filament. After more extended observation the 

 movement appeared to me to consist in a lateral deflection 

 and retraction of the thread. If the left hand, for instance, is 

 closed, and now the index-finger of the same hand is alter- 

 nately extended and bent, if the hand is not too plump, the 

 tendinous termination of the indicator muscle in its retraction 

 will be seen on the back of the hand to slip to the left side, 

 forming a curve, and to resume its former position on bending 

 the finger. This will give a very fair idea of what I saw at 

 that time. At last, however, having obtained a fresh supply 

 of this Oscillatoria, I observed, as I have since never failed to 

 do, in a filament of about six or eight joints, the most active 

 size, and therefore the most fit for observation, what I consider 

 to be its true motion. The thread suddenly began to spin 

 round, while the filament was set in active motion, passing 

 quickly out of the field with the corkscrew-like movement of 

 a very active vibrio. I have said, the thread suddenly 

 began to spin round — at least so it then appeared, though 

 further experiments have now convinced me, that the filament 

 itself revolves at the same time, as is the case with other 

 species of Oscillatoria — but its progressive motion only being 

 seen, the whirling movement seems to be confined to the 

 strongly-marked green axis or thread which divides the cells 

 longitudinally. I confess, on making this last discovery, the 

 pleasure I felt on first beholding, what I could but regard as 

 the locomotive apparatus of the filament, was greatly dimi- 



