94 JOURNAL OF THE fOctobcr, 



JV. viridis, and the single larger N. viridis was seen. But the 

 most unexpected thing noted was that seven Cyclops and Cypris, 

 and the young of the former, had gathered at the light spot. In 

 a moment the Cyclops scattered, but the Cypris kept on its lively 

 feeding and remained constantly within the spot admitting the 

 light. At other intervals during the day the Cyclops could always 

 be seen playing around or darting across the light spot, and early 

 in the day a few desmids appeared attached to little strands of 

 algge, and also a few large desmids — Micrasterias rotata and 

 Closterimn mottiliforme. 



At a time when the diatoms were noted as being quite abun- 

 dant, I arranged the microscope by bringing the tube to a hori- 

 zontal position, and placed the bottle upright between the thin 

 metal stage and the substage. I then was enabled to observe 

 the travelling motion of all the diatoms congregated within the 

 radius of the quarter of an inch circular opening admitting the 

 light directly through the centre of the liquid. A Beck & 

 Smith half-inch lens gave a sufficient magnification, of, say, two 

 hundred diameters, enabling me to view all of the diatoms, large 

 or small, while in active motion. This method of examination 

 has the advantage that the diatom is in actual contact with, and 

 is adherent to, a smooth glass surface, and, as its movement pro- 

 gresses in a straight line for the whole distance of a quarter of an 

 inch, the rate of movement can be timed by a watch. As this 

 was relatively slow, it will be needless to state how many seconds 

 were consumed in traversing the width of the opening. And as 

 there were quite a number simultaneously crossing, there seemed 

 to be no interruption to a continuous direct motion, as would 

 happen when a slide is examined in a horizontal position and 

 the field littered with particles of debris. When such is the 

 case the direct motion is usually interrupted. An obstacle inter- 

 cepting the path of the diatom causes it to reverse its propelling 

 power, whatever that may be. But in the bottle there was no 

 debris adhering to the sides, and the only obstacles to be en- 

 coun'ered were other diatoms travelling at will in the general 

 field. The desmids were never adherent to the glass, for if the 

 bottle was held in the hand on any occasion they were always in 

 a tremulous state, chiefly attached to minute threads of algae, 

 while the diatoms kept up a constant motion, always in contact 



