52 INVERTEBRATE ANIMALS. 
mectum. Indeed, a transition between the two forms is found 
in the so-called Trumpet-animalcule or Stevéor (fig. 14, 2), which 
can detach itself and swim about at will, at the same time that 
it is ordinarily fixed by its thinner extremity to some solid 
object. In Vaginicola (fig. 14, a), again, we have an animalcule 
closely related to Stetor, but having the body protected by a 
horny or membranous sheath. 
All the Zzfusoria we have been hitherto considering belong to a sec- 
tion of the class in which the surface is furnished with more or less 
numerous cilia. There are other forms, however, in which there are 
no cilia, but the body is furnished with a number of radiating filament- 
ous tubes, the extremities of which form little sucking-discs. Finally, 
there is another section in which the organs of locomotion are in the 
form of long contractile filaments, termed ‘‘ flagella,” which may be 
combined with cilia, or may be the only locomotive organs present (fig. 
12, ¢). In accordance with these differences, the //usoria are divided. 
into the three orders of the Ci/iata, Suctoria, and Flagellata, of which 
the ciliated forms are by far the most numerous and most important. 
DISTRIBUTION OF INFUSORIA IN SPACE.—<As regards the distribu- 
tion of Jzfusoria in space, there is little to say, except that they are of 
universal occurrence in fresh water over the whole globe, and that they 
occur also in the sea. In fact, the only conditions which appear to be 
necessary for their existence are a certain quantity of water holding or- 
ganic matter in solution. Wherever these conditions are fulfilled, 7/- 
soria are certain to make their appearance. The attached forms of 
Infusoria, however (such as Vorticella, Epistylis, Stentor, and others), 
do not appear to be ever developed in artificial infusions, and they are 
to be sought for on the stems of water-plants, and in other similar local- 
ities. It seems hardly necessary to remark that, as before defined, the 
occurrence of fossil Zz/fusoria is not to be looked for, as they possess no 
hard structures which are capable of permanent preservation. It is only 
to be added in this connection, that if the animalcule known as WVoctiluca 
be rightly referred to this class, the //usoria take a very decided share 
in producing the diffused phosphorescence or luminosity of the sea, 
which is occasionally such a beautiful spectacle even in our own cli- 
mate. 
TABLE SHOWING THE DIVISIONS OF THE PROTOZOA. 
Crass I. GREGARINIDA.—Parasitic Protozoa which are destitute of 
a mouth, and do not possess the power of emitting pseudopodia. 
Crass II, Ru1zopopa.—Protozoa which are destitute of a mouth, 
are simple or compound, and have the power of emitting extensile and 
contractile processes of the body-substance (pseudopodia). 
a. Monera,—£x. Protogenes. 
b, Amebea.—LEx. Amceba, Difflugia. 
