
322 WHAT IS A DESMID? 



































terpreted being producible at will by a particular adjust- 
ment of the illumination, but being undiscoverable when 
the greatest care is taken to avoid sources of fallacy.” Mr. 
Osborne also thought he had detected external apertures 
in the cell-wall of Closterium, at about the locality where 
Ehrenberg had placed his “prehensile organs,” or “feet,” 
which, of course, were necessarily present, whilst he con- 
sidered the Desmids as animals. Dr. Carpenter says with 
regard to this, “I must confess to a similar scepticism re- 
specting the external apertures said by Mr. Osborne to exist 
at the extremities of Closterium ; for whilst their existence 
is highly improbable on a priori ground, Mr. Wenham 
(than whom no observer is entitled to more credit) states 
that *not the slightest break can be discovered in the lami- 
nated structure that the thickened ends display." My ob- 
servations coincide exactly with those of the last gentlemen, 
and in fact the same is the opinion of all competent and un- 
prejudiced observers at the present day. Most, if not all 
the Desmids, have the power of changing their place by 
sailing, slowly it is true, through the water, though not ex- 
hibiting the liveliness so evident in the Diatoms. But 
that they do move can be shown by shaking them up with 
some mud, and then covering them with water in a saucer, 
and placing them where the ices sunlight, or even light 
reflected from the sky, can fall upon the surface, when, after — 
a time, it will be seen to become green, and the Desmids are |. 
found to have congregated at the point nearest the light; in 
this respect exhibiting their vegetable nature, for we know 
that plants love the light and vill tend towards it whenever 
a can do so. 
_ An individual of Closterium is represented in Plate 5» 
g . 10, and the vacuoles at the ends containing the motile | 
granules are there seen, as well as indications of the circu- - 
lation « of the cell-contents spoken of. The mode of growth 
and posite of the Desmids are very remarkable and 
> Tint we must leave the onsidorshian s | 













Sene 
