SPONGIDA. 75 
When cleansed it becomes flaxen-coloured and of a looser texture. 
ee of the great channels which traverse it are rough and 
ristly. 
The brown Barbary sponge, when first taken out of the water, 
presents itself as an elongated flattened body, gelatinous, and charged 
with blackish mud. It is then hard, heavy, coarse, and of a reddish 
colour. When well washed in water, it becomes round in shape, still 
remaining heavy and reddish. It presents many gaps, the intervals 
of which are occupied by a sinuous and tenacious network. It is 
valuable for domestic use, because of the facility with which it 
absorbs water, and its great strength. 
Other sorts of sponges are very abundant. The Blonde Sponge 
of the Archipelago, often confounded with the Venetian ; the Hard 
Barbary Sponge, called Gelina, which only comes by accident into 
France ; the Salonica Sponge is of middling quality; finally, the 
Bahama Sponge, from the Antilles, is wanting in flexibility, and is a 
little harsh, and so is sold at a low price, having few useful properties 
to recommend it. 
Many species of Sponge are described as inhabiting the British 
seas, but none are of any commercial value. 
No very satisfactory classification of the Sponges has as yet been 
made, although many recent writers have attempted with more or 
less success to arrange the very numerous forms now known into 
definite groups. Among these we may mention Dr. J. E. Gray, Dr. 
Bowerbank, and Professor Oscar Schmidt. With a few exceptions, 
all sponges, as we have seen, contain spicules; these are either 
siliceous or calcareous. We may therefore divide the sponges into 
two sections, the first being called 
CALCAREA. 
Skeleton chiefly composed of calcareous spicules, which are 
generally three-rayed. All the species are marine, and none appear 
to attain large dimensions, while some of the very smallest sponges 
known belong to this section. Grantia compressa, one of our com- 
monest British sponges, will serve as an example. 
SILICEA. 
Skeleton mostly horny, most frequently strengthened with 
siliceous spicules ; these sometimes absent; and, in at least one genus, 
the sarcode becomes not even differentiated into a horny skeleton. 
The sponges belonging to this section are found both in fresh and 
