SPONGES 
(Porifera), 
The commercial Sponge, when alive* contauis, besides 
the horny skeleton with which everyone is familiar, soft tissues 
of an intricate structure. Its surface is full of small pores 
which lead into a much-branching system of canals and cham- 
bers. Water conveying oxygen and food in the form of minute 
organisms is taken into these canals, is then driven along by 
the whip-like processes of the cells lining the chambers and 
finally leaves the body by large openings called 'oscula' carry- 
ing with it any waste products there may be. The name 
Torifera' by which Sponges are scientiBcally known, refers to 
the pores and oscula by which their surface is perforated. 
The sponges of commerce are obtained principally in the 
West Indies, in the Adriatic and the eastern portion of the 
Mediterranean. After they have been collected their soft parts 
are removed by a careful process of maceration^ leaving a 
horny and highly elastic skeleton. No Sponges of the finest 
qualities seem to occur in these waters, but there are many 
coarse kinds of Horny Sponges on the local coral reefs. They 
have a slimy surface arid may be dark brownish green or 
purple or almost black in colour. In some species of Sponges 
the horny fibres contain sand grains and other impurities picked 
up from the bottom of the sea, others contain siliceous spicules 
which have been manufactured by the sponge itself. In other 
sponges again the horny fibres are absent altogether, and the 
skeleton consists merely of masses of siliceous spicules, 
arranged into regular strands or scattered loosely through the 
soft tissues, the spicules being of an almost endless variety in 
shape and size. In a few Sjwnges the skeleton has entirely 
disappeared : these are small and slimy species, generally for- 
ming a mere coating on stcmes and other objects. Finally 
some Sponges have a skeleton made of spicules of carbonate of 
lime. The siliceous spicules may be in the shape of rods, need- 
les, pinst anchors, stars, crosses etc., and form beauiiful micros- 
copic objects. The calcareou<? spicules are simpler, one, three 
and four-rayed only. 
