5 62 
THE LOWEST ANIMALS. 
is formed of radiating spines of a horny nature. The first group is subdivided into 
three sections, according to the characters of the central capsule. In the first 
section the capsule is spherical and uniformly perforated by numerous small pores; 
in the second conical, with a perforated sieve-like floor area below; and in the 
third it has one main aperture and one or a few accessory ones, and is surrounded 
by a dark pigment. In the forms with a siliceous skeleton the geometrical 
pattern of the skeleton conforms more or less to the shape of the central capsule, 
being either spherical or conical. The central capsule is regarded as being 
homologous with the calcareous shell of Globigerina. Reproduction takes place by 
simple division into two, or by the breaking up of the body-substance into oval 
spores, each provided with a flagellum or whip. Two spores, which may be of 
similar or of different size, fuse together; the resulting individual growing into 
an adult radiolarian. Certain yellow corpuscles present in the outer part of the 
body of surface radiolarians are unicellular parasitic algae, which can be separated 
and cultivated independently of their host. The radiolarians live floating at 
all depths. Some forms are abyssal, living in depths of one thousand to two 
thousand five hundred fathoms. Over certain areas in the Central Pacific and the 
south-eastern part of the Indian Ocean the ooze forming the ocean-bed is chiefly 
made up of their skeletons, sometimes to an extent of eighty per cent, of the deposit, 
which has hence been termed radiolarian ooze. The chalky-looking rock, known 
as Barbados earth, a Tertiary formation, is composed almost entirely of skeletons 
of radiolarians. Somewhat similar deposits exist in the Nicobar Islands, in 
Greece, and in Sicily. Fig. 1 of the Plate shows the elegant lattice sphere of 
Rhizosphcera. Fig. 2 represents Sphcerozoum, whose skeleton consists of loose 
spicules, arranged tangentially. Actinomma (Fig. 3) possesses three concentric 
lattice-spheres, joined by radiating spikes. Fig. 7 represents a deep-sea form 
(Ghallengevict), whose oval case is formed of a regular, very fine-meshed network. 
Fig. 8 depicts the elegant lattice-sphere of Hdiosphcera ; while Lithomespilus, 
Ommatocampe, and Carpocanium are shown in Figs 4, 5, and 6, and Clathrocyclas 
and Dictyophimus in Figs. 9 and 10. 
The Infusorial Animalcules, —Class Infusoria. 
The name Infusoria, which came into use a hundred years ago, was applied 
to certain tiny living specks which appeared in infusions of hay, etc. The animal¬ 
cules so named were classed with the worms and radiated animals, or zoophytes. 
As the microscope improved, infusorians were found to possess a considerable 
amount of structure. Ehrenberg attributed to them a highly complex organisa¬ 
tion, supposing them to possess intestines, nervous system, etc. Later observations 
negatived these views, and showed them to be animals formed of one cell or 
composed of a colony of one-celled individuals. It is true that this cell, or unit- 
mass of protoplasm, may show a wonderful amount of differentiation, what with its 
nucleus, contractile vacuole, mouth and gullet, its variously arranged cilia or flagella, 
its contractile fibres, its separation into an outer denser and an inner more fluid 
protoplasm, and its horny cups, stalks, etc. Most of the species here described live 
in ponds and ditches, the larger forms preferring clear to stagnant and muddy water. 
