S2 THE AMERICAN MONTHLY [April, 



being also reversed at the same time. The same thing occurs in all fil- 

 aments of whatever length, the whole filament travelling a certain time 

 in one direction and then reversing its motion : the rear end apparently 

 travelling as fast in the same direction as the front end. though of course 

 there must be a slight difference due to cell division or growth, but it 

 is so small as to be unnoticeable. The rapidity of axial revolution 

 varies greatly in difterent varieties, some moving onward a considerable 

 distance before completing a revolution, in others the revolving motion 

 is the most rapid ; some of the minute varieties found in the brackish 

 water of salt marshes revolving with great rapidity, while the onward 

 motion is comparatively slow. Spirulina tcnuissima makes one or 

 two complete revolutions per second. 



When the end of a long-moving filament strikes an obstruction the 

 moving impulse is sufficiently powerful to cause the filament to bend 

 or double up, and the revolving motion may cause it to twist upon itself 

 or others so as to resemble the strands of a rope, but it generally works 

 itself free and resumes its natural position. In all cases under my obser- 

 vation the waving or nodding movements of which so much has been 

 written are caused simplv bv the elasticity of the filament springing out 

 to regain its normal position wdiile working itself free from obstructions. 

 The proper motion is an onward spiral movement forward and back- 

 ward in the direction of its length, thus showing a striking resemblance 

 to the motion of diatoms and probably produced in a similar manner. 



When a tuft of active Oscillaria is placed in water in^ shallow dish 

 and exposed to light the filaments are free to move in all directions 

 away from the central mass. Returning, they meet obstructions ; con- 

 sequentlv they move a little further in one direction than in the other. 

 Thus their rate of speed over the dish, instead of showing their true 

 rate of motion, onlv shows the excess produced by free motion over 

 that retarded. To detect the axial revolution of some varieties requires 

 very close observation. I do not at present propose to advance any 

 theory as to the cause of motion, but simply record my observations 

 and my conviction that the movements of Oscillaria, like those of 

 diatoms, are entirely distinct and separate from those due to growth. 



The Oscillaria are very plentiful in the salt marshes. The filamentous 

 growth, mentioned in a former article as covering the active groups of 

 Bacillaria paradoxa,, appears to have been Leptothrix tinctorid. I 

 found a class of many varieties, from the minute Spirulina tcnuissima 

 up to those as large as the filamentous desmids, which I do not recog- 

 nize in Mr. Wolle's illustrations, with the exception of the Spirulitta. 

 They were colorless, and I should have supposed them in advanced 

 stages of growth, but their very active movements seemed to preclude 

 the idea of old age ; one of them was as large as Ilyalothcca dissilicns 

 and somewhat resembled it in outline, excepting that the cells were 

 rounded and not notched, and appeared to have a division in the centre. 

 Thev were hyaline with the exception of small, irregular, opaque patches. 

 Opposite ends of some of these filaments were sometimes moving in 

 opposite directions, so as to bend or double up the filament into a sig- 

 moid form, and as the ends approached each other the motion would 

 reverse. 



When the end of one of these filaments suddenly obtrudes itself into 

 the field of the microscope it bears a most startling resemblance to an 



