Many are
microscopic, and belong to the class of animalcules called _Infusoria_.
A very remarkable quality which the Infusoria possess--one very useful
for the aquarium, and one which would seem to settle their place in the
_vegetable_ kingdom--is that they _exhale oxygen_ like plants. This has
been proved by Liebig, who collected several jars of oxygen from tanks
containing Infusoria only.
A piece of honeycomb coral (_Eschara foliacea_) is easily found, and,
when well selected and placed in the aquarium, may continue to grow
there by the labors of its living infusorial tenants: they are not
unworthy rivals of the Madrepores, or deep-sea coral-builders of warmer
latitudes. The walls of its cells are not more than one-thirtieth of an
inch in thickness, and each cell has its occupant. So closely are they
packed, that in an area of one-eighth of an inch square the orifices of
forty-five cells can be counted. As these are all double, this would
give five thousand seven hundred and sixty cells to the square inch. Now
a moderate-sized specimen will afford, with all its convolutions,
at least one hundred square inches of wall, which would contain a
population of five hundred and seventy-six thousand inhabitants,--a very
large city.
Pages:
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227