





























WHAT IS A DESMID? 319 
in some cases, is very broad, but in others is extremely 
thin. 
The outline of the Desmids, although always preserving a 
more or less perfect bilateral symmetry, varies very greatly. 
Thus in Closterium, a genus of very general distribution, 
and one at the same time which includes a great number 
of species, the general form is a round tube, more or less 
pointed at both ends, and with the apices both bent over in 
the same direction so that the individual is somewhat moon- 
shaped, or more like two cows’ horns united base to base. 
When Closterium is examined with care by means of a good 
microscope, it is found to have its bright green cell-contents 
arranged longitudinally in seeming uncertain bands, which 
coalesce more or less, and hence are not always to be dis- 
tinguished. But at the ends of the frustule are to be seen 
apparent organs of wondrous characters, and whose office 
has not as yet been determined. And the extreme minute- 
hess of the whole plant presents great difficulties to its 
proper study, so that it is hardly to be wondered at that the 
functions of its integral parts should not be thoroughly com- 
prehended. These seeming organs are spaces or vacuoles 
Separated from the rest of the cell-contents, and generally 
of a spherical form, transparent and colorless. Within 
them, however, are observed numerous minute granules 
formed of a material of different density, as is shown by 
their effect upon light. And these are continually, in the 
healthy individual, in motion, moving about with a trem- 
bling and seemingly excited action, putting one in mind of 
the swarming of a crowd of bees, and hence it is often spo- 
ken of as swarming. Besides this, however, there is still © 
another kind of motion to be seen within the Closterium 
cell-wall, and one at the same time perhaps of greater won- 
der and perplexity than that already mentioned, as the mode 
of motion is a problem as yet unsolved. This is the siren: 
lation or rotation of much of the liquid contents of the in- 




