Wlarvels of the Universe 907 
vegetable matter. Again, chemical analysis has 
shown that the composition of sponge is very little 
different from that of silk, which is definitely an 
animal substance. 
As regards the appearance of sponges, there are 
so many different varieties and forms that it would 
be impossible to enumerate them all ; in fact, it has 
been well said that by reason of the wide diversity 
of forms sponges might with equal justice be con- 
sidered formless. Some, like the ‘Crumb of Bread” 
Sponge, will cover the surface of flat rocks with 
ranges of miniature volcanoes ; others, such as the 
Tree Sponge, also of our own shores, divide up into 
branches with strong suckers, by which they are 
attached to the rock. Others are spherical and 
entirely unattached, and are rolled about on the sea- 
bed by the motion of the waters, the toughness 
and elasticity of their fibre protecting them from 
damage. 
There is a species of Glass Sponge which exactly 
resembles a mushroom, while yet another sponge is 
merely a floating mass of fine white and semi-trans- 
parent tubes united together by a loose network, and 
other strange varieties are illustrated in these pages. 
But the best-known forms of sponge are the “ Cup ”’ 
Sponge and the Bath Sponge of commerce. The first, 
as its name implies, is cup-shaped, of very fine 
texture and innumerable small apertures. It is 
sometimes called the Common Bath Sponge, is 
altogether more loosely knit, has larger apertures and 
no very definite shape. Every sponge in its natural 
state is covered with a thick gelatinous membrane, 
entirely concealing the fibrous material which is 
usually recognized as ‘‘ a sponge’ (but which is really 
only the skeleton of a sponge). In this flesh is stored 
the protoplasm that goes to build up the wonderful 
structure; it is a thick, milky and glutinous sub- 
stance, and has to be extracted before the sponge 
can be placed on the market, for it quickly putrefies 
as soon as the living organisms composing the fabric 
are destroyed; the process of extraction is called 
~ taking the milk out” of a sponge. 
In spite of its lowly position in the scale of animal 
life the structure of a sponge is very complex. The 
material which composes the cup may be divided 
into two sections, the outer or fleshy part, and the 
inner or fibrous part. The body tissues are com- 
posed of various kinds of cells, some of which assist in 
the process of nutrition, while others are employed in 
A STALKED SPONGE. 
This beautiful Sponge has a thick main stem with 
three branches. From these branches rise spiral blades 
of sponge-tissues diminishing in size as they ascend. 
