68 THE OCEAN WORLD. 
them the substances necessary to the nourishment of these strange 
creatures, and at the same time carry off all excremental matter. At 
the same time, the walls of these canals present a large absorbing 
surface, which separates the oxygen with which the water is charged, 
and disengages the carbonic acid which results from respiration. 
Again, Dr. Johnson omitted them altogether from his work on 
“British Zoophytes.” ‘If they are not the production of polypi,” 
he says, “the zoologist who retains them in his province must contend 
that they are individually animals, an opinion to which I cannot 
assent, seeing that they have no animal structure or individual organs, 
and exhibit not one function usually supposed to be characteristic 
of the animal kingdom.” Gervais and Van Beneden consider, as 
Milne-Edwards does, that the embryos are at first movable, then 
fixed, many of them uniting together, and melting, as it were, into 
one common colony, which becomes a sponge, such as we see it. An 
isolated embryo might also, by throwing out germs, produce a similar 
colony, which would thus become a product of agamous generation. 
Thus it appears that Science is far from being settled in its views as 
to the organisation and development of these obscure and complex 
creatures ; nor is it more advanced in its knowledge of the duration 
of life and the quickness of growth in sponges. 
It is not to be denied, also, that these beings constitute, in spite 
of the investigations of modern naturalists, a group still somewhat 
problematical as to their position in the scale of animal life, and 
that they are still very imperfectly known as regards their internal 
organisation. 
Some sponges form masses of a light elastic tissue, which is, at 
the same time resistant. The number of species or supposed species 
at present known is very large. Dr. Bowerbank, in his work 
on “British Sponges,” published in 1866, describes nearly 200; 
and many species have been since added to our Fauna. They are 
met with presenting every possible diversity of size and outward 
configuration. Many of them are very small, others are of immense 
size. Neptune’s Cup (Raphiophora patera, Gray) is met with oft 
Singapore, and forms an immense mass, upwards of three or four 
feet in height. The skeleton of sponges is usually composed of 
horny, anastomising fibres (Fig. 9). In some sponges, as Grantia, 
this is altogether wanting. In others again, as in Pheronema, the 
skeleton is chiefly composed of siliceous fibres. Calcareous or siliceous 
bodies, called spicula, are met with in most sponges, and vary very 
much in form and size. Many of these form most beautiful and 
attractive objects for microscopic examination. Every one is familiar 
