PoKiFERA . RAD I AT A. Calcarba. 405 
only a sort of horny skeleton, on which the true living 
portion of the sponge is supported. This consists of 
a gelatinous matter, which is spread over all the fibres 
of the reticulated skeleton ; its consistence is very like 
that of the white of an egg, and it runs freely away 
from the sponge when the latter is taken out of the 
water. This gelatinous substance resembles that of 
which the Amceba, one of the Khizopoda, is composed, 
and apparently consists of minute masses of aggregated 
sarcode cells. Each of these cells appears to possess 
an independent existence ; those on the surface beiiig 
furnished with long and very slender vibratile cilia. 
If we take a piece of common sponge, we see that 
its surface is every where perforated with an infinite 
number of minute holes, amongst which a considerable 
number of large openings are scattered. When this 
sponge is examined in a living state, a rapid stream 
of water may be observed issuing constantly from these 
larger orifices. This excurrent stream of water is ren- 
dered observable by the fact, that it bears with it a 
number of minute particles from the interior of the 
sponge. This water is imbibed through the minute 
pores distributed in such profusion over the entire sur- 
face of the sponge. After passing through these, and 
traversing the cavities formed in every direction by 
the reticulated structure of the mass, it is collected into 
canals, hy which it is finally conducted to the larger 
openings of the surface. The objects of this continual 
flow of water are for nutrition, for the expulsion of 
digested particles, for respiration, and assisting in the 
propagation of the species. 
The propagation of the species is effected in various 
wa}'s. They are propagated by division ; when cut 
in two, the two portions will each grow and become 
perfect sponges. They are also, and more usually, 
propagated by gemmules, which sprout from the deli- 
cate granular film covering their skeleton, and which, 
as they gradually become detached from the parent 
body, are furnished with cilia, swim freely about, like 
infusorial animalcules, and afterwards, finding a favour- 
able locality, become fixed and eventually develope into 
perfect sponges. In a third case, propagation takes 
place by seedlike bodies being produced in the sub- 
stance of the sponge. At first these consist of several 
cells merely united together into a globular or ovoid 
mass, lying freely in cavities of the substance of the 
sponge. This mass of cells then becomes enveloped 
in a capsule. When these cells are pressed out of the 
cavity of the capsule under water, they soon swell up 
and burst, and the germs contained in them gradually 
become diffused over the bottom of the vessel. In 
a few days these collect into separate groups, each 
inclosed in a mucilaginous substance. From these 
germs active animacules are produced, possessing a 
power of locomotion by the extension of different 
parts of the body. They exhibit considerable acti- 
vity, asume at times fantastic forms, and are very 
voracious, absorbing other minute animals into their 
substance, in the same manner as has been observed 
in the Amsebse amongst the Ehizopoda. 
Sponges vary much in form, and are for the most 
part fixed by a kind of root at the base, and attach 
themselves to almost every body which can afford them 
support, whether fixed or floating. Many are found 
encrusting submarine objects, as stones, shells, rocks, 
&c. They are mostly marine, only comparatively few 
being found in fresh water. In the living state, many 
of them possess lively colours, and usually grow in 
groups. They occur in all seas, from the equator to 
the pole. A peculiar group of sponges, belonging to 
the genus Cliona, are peculiar for the habit they have 
of boring. Shells, other submarine bodies, and even 
rocks, are penetrated by these unobtrusive-looking 
animals ; and they effect a powerful action upon these 
bodies by slowly and silently producing complete dis- 
integration. There are three kinds of sponges, each 
of which is composed of many species, and form as 
many orders or divisions : — 
THE HORNY SPONGES [Cornea) are distinguished 
by having no spicula, and have the body very porous 
and elastic, soft, and composed of a fibro-corneous 
skeleton, which anastomoses in all directions. 
Genus Spongia. — This genus is the type of this 
group ; and in it is contained the common sponge of 
commerce. The sponges of commerce are obtained 
in considerable abundance from the Mediterranean, 
and are usually prepared for use by soaking them in 
dilute hydrochloric acid, in order to remove all traces 
of lime, and then bleached and well beaten to render 
them fit for market. The inhabitants of some of the 
Greek islands have been trained from their infancy to 
dive for these substances. They adhere firmly to the 
bottom, and are not detached without a great deal of 
trouble. Smyrna is the great market for sponge. 
THE SILICEOUS SPONGES [Silicea) have the body 
more or less rigid or friable, and strengthened with 
siliceous spicula. The group is represented by the 
genus Thethys. 
THE CALCAREOUS SPONGES [Calcar ea) have the 
body, which is not very soft, and composed of a sub- 
cartilaginous substance, supported by calcareous spicula. 
The genus Grantia is the type. 
END OF RADIATA. 
