158 MEMORANDA. 



From bein^ somewhat limited in a supply of the Clostermm 

 lunula, I have used the C. acerosum as the chief subject of the 

 investigation, from the fact that all the motile phenomena are 

 precisely analogous, and quite as easily marked as in the 

 other. 1 possess a white flint glass bottle (closed with a cork), 

 containing an aquatic plant. The earth at the bottom is 

 covered with a stratum of the C. acerosum, and each decaying 

 stem of the plant, is also sheathed with a bright-green coating 

 of the same, in a vigorous state of growth. Specimens in 

 various stages taken direct from this source, were the objects 

 observed. 



In the C. acerosum, the endochrome and primordial utricle 

 will sometimes be found partly contracted in a longitudinal 

 direction, at the same time drawing the swarm-spores and va- 

 cuole with it ; a considerable clear space is thus left at the end 

 of the frond, wherein the motion of the protoplasm can be very 

 distinctly seen in the act of flowing and returning in thread- 

 like currents, which shift their position, and frequently take 

 a spiral direction, in a manner exactly resembling the circula- 

 tion in the hairs of some plants. 



The vital protoplasm contained within the Desmidiece, has a 

 similar granulated appearance, and is endowed with the same 

 active powers of locomotion as in other plants. Having 

 then a tendency per se to run in rapid currents, why should 

 the presence of cilia be requisite for assisting a motive 

 force already sufficiently energetic ? Without being pre- 

 judiced by any obvious reply to this question, I have tried to 

 discover the presence of cilia, with the aid of the most perfect 

 appliances that the optician's art can furnish, but without 

 success. So far as eyesight will inform me, there are no 

 indications of these organs either externally or internally — 

 neither on the membrane of the primordial utricle, or as an 

 investment, lining the inner wall of the frond — all the undu- 

 lating motions and currents appear to be caused entirely by 

 the movements of the protoplasm. 



As I can, at will, adjust the illumination, conjointly with 

 other circumstances, so as to produce the most positive ap- 

 pearance of moving cilia, not only internally, but also on the 

 exterior of the frond, I will briefly mention the causes of this 

 fallacy. The effect of oblique sunlight, or any other powerful 

 source of illumination, in causing a refractive atom to appear 

 elongated, as a ray or line, is too well known to need comment, 

 as is the fact that this ray will appear to extend over the boun- 

 dary of a cell-wall, or other adjoining body. Another cause 

 of deception arises from a large angle of aperture ; when a thin 

 plane or membrane is viewed, in such a position as to be 



