186 Transactions of the Society. 



made as it were the radii of a quadrant of a circle of which tlieir 

 fixed point is the centre ; and by the rapid movement of the body- 

 to and fro in the circumference of the arc, the body was as many 

 as thirty times per minute made to act hammer-hke upon minute 

 particles of decomposing matter. But in this organism, what was 

 apparently the same result, was brought about in a manner wholly 

 ditferent. 



The organism was never attached — had no power that I could 

 discover of attaching itself for a moment ; but by a free darting, down 

 upon, and away from, minute particles of decomposing matter by 

 the organism in large numbers, such matter was visibly, in the 

 course of half an hour, reduced in size and altered in shape. 



Fig. 9, plate IV., will give an idea of this mode of movement : 

 a represents a minute particle of decomposing debris, and the arrows 

 placed beside the organisms indicate the direction of motion. 



Each one in turn, in a space of time occupying about two 

 seconds, comes into contact with the particle a, and at once recedes 

 to a distance of four to five times the length of the flagella, and 

 instantly again darts upon the object, and this may be continued 

 by given forms for hours. 



No sight accessible to the human eye can be more fascinating or 

 more beautiful than this, with delicate illumination and such defi- 

 nition as we can now obtain. 



Fifty or even a hundred may be observed with ease, in one 

 field, pursuing their untiring work. It is the more entrancing that 

 it is apparently rhythmic, not like the measured march of a regi- 

 ment, but the rhythmic movement of a peal of bells. 



But the method in which the motion, with its manifest force, is 

 brought about, is a matter of greatest interest, and the discovery of 

 which is fraught with much difficulty. 



The extreme minuteness of the organism, the large number of 

 its delicate flagella, and the intense rapidity of its movement, are 

 the three factors of difficulty. 



It is absolutely needful first to familiarize oneself with its 

 general movements before interpretation of this special action can be 

 hoped for. 



In swimming, and in the wave motion I have described, figs. 

 1, 2, 3, plate IV., and 1 and 4, plate V., all the flagella may be, 

 with care, clearly seen ; but in the act of darting down upon, and 

 away from a piece of debris it is otherwise. Fig. 9 h, plate IV., 

 shows one of the forms at the very moment of impact: all the 

 flagella are behind, and (in this instance with the 1/12 objective, 

 l-iT N.A.) a spiral form is indicated in the arrangement of these 

 flagella. 



At c in the same figure, one of the forms, having accomplished 

 impact, is receding. Two of the flagella now fall to the front. 



