506 DESMIDS AND DIATOMS. 
isms, and that names devised to represent their supposed 
characters, but calculated to lead into constant error, 
should thus have been perpetuated. The name of Infu- 
soria, applied to the whole assemblage of animated forms 
first revealed by the microscope, was derived from the in- 
variable presence of these bodies in all infusions of decay- 
ing animal and vegetable matters. It is to their rapid ap- 
pearance and development under circumstances calculated 
to remove or destroy all germs of organic life, that the 
doctrine of spontaneous generation, still maintained by 
many able observers, owes its origin. Into the character 
and habits of the Infusoria proper, or Protozoa, as they are 
now called, as well as those of the Rotatoria or Wheel- 
animalcules, I do not now propose to enter. Suffice it to 
say, that the two remaining families, the Diatoms and Des- 
mids, after repeated tossing from the one kingdom to the 
other, are now universally admitted into the department 
of the botanist, and can really have nothing in common 
with that of the zodlogist. 
The Desmids and Diatoms were grouped together by 
Ehrenberg, under the single name of the Bacillariæ, from 
bacillum, a rod or wand, a name singularly inappropriate 
as applied to the whole family, including as it does a 
large proportion of forms having no such resemblance. 
By naturalists of later years the two are included as co- 
ordinate suborders of the minuter Cryptogamia, termed 
Alge by botanists. 
The Desmids, or Desmidiacez, so called from the par- 
tial division of the single cell of which they consist into 
two by a deep constriction in the middle, which is highly 
characteristic of the whole family, are pseudo-unicellular 
alge of a beautiful green color and great variety in size 
and outline. Unlike the Diatomacee, they are confined 
