68 THE OCEAN WORLD. 



them the substances necessary to the nourishment of these strange 

 creatures, and at the same time cany oft" 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 Zooph3'tes." " 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 hfe, 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 si)onges, and vary very 

 much in form and size. Many of these form most beautiful and 

 attractive objects for microscopic examination. Every one is familiar 



