' 64 
the distinction being made too stringent, into horny, si- 
and calcareous sponges. The toilet-sponges 
belong to the first class. The horny filaments are 
arranged in layers, and form a more or less dense 
network. In the calcareous and siliceous sponges 
spicules of lime or flint are embedded in the animal 
substance. These are often of a pure white, and of 
liceous, 
elegant forms, resembling needles, hooks, anchors, 
spiny balls, spades, walking-sticks, and many other 
figures, alternating with cross-bars, in the middle 
Order I. 
Toilet-Sponge (Sfougia usitatissinta) 

Section of a horny sponge, 
Its skeleton consists ex- 
Order II. 
In these, we find siliceous deposits of various 
forms, often intermixed with horny substance. 
Plate XXX. fig. Axinella polypotdes is one 
of the few forms which possess a fixed axis resembl- 
ing that of a colony of polyps. The number of 
separate individuals of which the colony consists is 
indicated in the figure. 
typical of this Order. 
To the siliceous sponges belongs the Fresh- 
water Sponge (Sfongilla fluviatélis) which consists of 
a greyish-brown crust over old woodwork, &c., in 
water, which is easily rubbed off. Its spicules under 
Order Ill. Calcispongia. 
Here the skeleton consists entirely 
careous spicules, which are either simple, 
4-armed. All the forms occur in the 
of cal- 
or 3- or 
same species. 
Subkingdom 
The Protozoa occupy the lowest place in the 
Animal the Vertebrata occupy the 
highest. As we descend the scale we mcet with simpler 
Kingdom, as 
and simpler organisms. We find organs which form 
an independent system in the bigger animals, such aS 
the circulatory system, growing gradually simpler and 
less-distinct, till they unite at last with a wholly different 
system, as in the body-cavity of the Celenterata, 
both for and 
Complication of organisation corresponds to compli- 
cated conditions of life. 
which serves digestion circulation, 
In the higher animals, the 
function of reproduction is confined to the sexual 


Ceraospongdia. 
Halichondria. 


| 

of which 
needles. 
These spicula are sometimes scattered through 
the animal substance, and they are sometimes united 
into a firm skeleton which forms a faithful outline 
of the sponge, after the animal life has departed. 
The sponges are almost exclusivey marine, and some- 
times produce eggs, which develop a larva which 
swims freely for a short time, and sometimes increase 
by budding. 
rises a small tree, with long clustered 
(Horny Sponges). 
clusively of elastic horny filaments, which form a 
network, which sucks up water into its many empty 
channels. Sponges are used for different purposes 
according to the firmness of their tissues. The sponge- 
fishery is carried on chiefly on the coasts of Dalmatia 
and Turkey, partly by divers, and partly by up- 
rooting the sponges with tridents, from a boat. The 
sponges are first kneaded till all the slimy animal sub- 
stance which overlays and pervades them, is removed, 
when they are washed clean with water. The sand which 
they usually contain afterwards is only a fraudulent 
addition to increase the weight. Latterly attempts 
have been successfully made to propagate spones 
by artificial division. 
(Siliceous Sponges). 
the microscope form fine slender spindles, sticking 
together, and forming a delicate network. 
iigeats Euplectella aspergillum, Venus’s Flower- 
Basket, is one of the most beautiful of the Vitreous 
Sponges, in which the siliceous deposits form a firm 
skeleton. When the animal substance is removed, 
the skeleton forms a long tube of the purest white, 
about nine inches long, and latticed in at the top as 
well as at the sides. The lower end of the tube is 
fixed in the sand, and is surrounded by a long tuft 
of fine needles, which look like spun glass. It is a 
native of Japan. 
(Caleareous Sponges). 
are single, 
figured. 
Many calcareous sponges 
as is Scandra ciltata, here 

Protozoa. 
organs; but in the lower animals a new animal may 
arise from any part of the body by budding or fis- 
repro- 
causing 
sion. Among the lower animals sexual 
duction alternates irregularly with asexual, 
the naturalist much perplexity in following out the 
life-history of the animal. In the lowest animals 
sexual reproduction disappears altogether, and the 
Protozoa multiply by subdivision. But the chief 
feature in which they differ from other animals is in 
the simplicity of their structure. We seek in vain for 
such as nerves, mus- 
animals, even in the 
any trace of separate organs, 
cles, skin, &c. In all other 
