Natural History of the Animalcules. 117 
have been heated above the boiling-point of water, and 
yet have survived. The Infusoria are very widely distri- 
buted, being found everywhere in fresh or salt water, es- 
pecially where decaying matter is present, and where life 
conditions are favourable. They are usually microscopic, 
and some of the most minute forms of life known are mo- 
nads of the flagellate Infusoria. Many of the ciliate forms 
have very striking shapes, and are commonly denoted by 
the terms of their resemblances, such as the Bell-animal- 
cule, the Slipper-animalcule, the Trumpet-animalcule etc. 
The minute organism, Notliluca, to which the diffused 
luminosity or phosphorescence of the sea is due, is es- 
sentially nothing but a flagellate Infusorian. 
So far we have discussed in a brief and popular man- 
ner the stru6ture, the life history, and the general 
nature and affinity of the Animalcules — those different 
types of minute and lowly organisms which techni- 
cally are known as the Protozoa. It is but fitting 
to conclude with a short outline, in general terms, of the 
part they are playing, and have played, in Nature ; and 
this will serve, in a sufficient manner, to illustrate their 
importance. 
In all climes and at all depths, the ooze, covering and 
forming the bed of the sea, consists largely of the re- 
mains of the Animalcules. In extensive tropical areas, 
indeed, this ooze is essentially little more than the ag- 
gregated tests of Foraminifera and Radiolaria, though 
the relative proportions of these vary considerably. In 
the warmer and shallower waters, the Foraminiferal re- 
mains, chiefly those of the organism, Globigerina, al- 
ready referred to, predominate to such an extent that the 
ooze is described as being " Globigerina ooze ". The 
