238 
OOMPAfllSON BETWEEN ANIMALS AND PLANTS. 
stances ; it consists of a fibrous mass, containing a jelly-like 
substance, which, when touched, discovers a slight sensation, 
the onlj sign of life manifested by it. There are many species 
of sponge ; those most valued in the arts are found in the Med- 
iterranean Sea, and Indian Ocean. Some grow upon rocks, and 
are found covering the interior of submarine caves. The Spon- 
gia parasitica is seen growing upon the back and legs of a 
species of crab ; sometimes as many as forty individual sponges 
extend themselves over the crab impeding the motion of its 
joints, spreading like a cloak over its back, or forming for its 
head grotesque and towering ornaments, from which the poor 
erab vainly attempts to disencumber itself. Some species of 
the sponge grow to a very large size ; one has been found in 
the East Indies in the form of a cup capable of containing ten 
gallons of water. The fibrous part of the sponge is the skele- 
ton of the animal ; the large apertures (see Fig. 158, h) serve 
to carry out fluids from within ; while the water by wh'.ch the 
animal is nourished, is imbibed by minute pores : this contin- 
ual circulation of water is one of the most important functions 
of the living sponge. These animals resemble plants in their 
manner of producing others ^ they form a species of germ, like 
the bud growing upon the stalk ; this falls from the stem and 
becomes a perfect animal. If a part of one of these animals 
be separated from the rest, it will, itself, be as perfect a living 
animal as was the whole before. A polypus can be divided 
into as many animals as it contains atoms ; some of this order 
are very properly called hydras (many-headed). Besides these 
there is another order of animal substances, infusoria^ which 
appear like a homogeneous mass, having no appearance of any 
limbs whatever ; these are either angular, oval, or globular. 
Manner in which these animals are reproduced — Recapitalatioa. 
