SPONGES. 



767 



Yet, no one can form an adequate idea of the living Sponge from the dry, dead skel- 

 eton which is sold under that name. Many of the species are decked with delicate 

 colors, while all are truly beautiful creatures when viewed in full life and action. They 

 are to be found widely distributed through the seas, and there is hardly a solid body on 

 which a Sponge will not grow. Sponges are generally found hanging from the under 

 sides of projecting rocks at some distance below the surface of the sea, or clinging to 

 the roofs of submarine caverns. Some, however, are strong, sturdy, and branched, and 

 stand boldly erect like the earth-plants which they so wonderfully resemble. 



Even the living inhabitants of the sea are liable to become the resting-places of many 

 a Sponge, and the Crustacea are often forced to bear on their shells the additional burden 

 of living Sponges and other zoophytes much more massive than their whole body. 



The true living being which constitutes the Sponge is of a soft and almost gelatinous 

 texture, to the unaided eye ; and with the aid of the microscope is found to consist of 



Grdntia coarctata. 

 (New species.) 



Greuttia comfretta. 



an aggregation of separate bodies like those of the Amoebae, some of which are fur- 

 nished with long cilia. By the constant action of the cilia a current of water is kept up, 

 causing the liquid to enter at the innumerable pores with which the surface is pierced, 

 and to be expelled through the larger orifices. A Sponge in full action is a wonderful 

 sight : the cilia drives the water in ceaseless torrents, whirling along all kinds of solid 

 particles, arresting those which are useful for digestion, and rejecting those which it 

 cannot assimilate. 



The reader will at once see that a creature thus composed will stand in need of some 

 solid framework on which the delicate fabric can be supported ; and on examining a 

 series of Sponges with the microscope, we find that it is mostly composed of a fibrous 

 and rather horny network, strengthened with spiculae of a hard mineral substance. 

 The shape of the spiculas is extremely variable, some being simple translucent bars, 

 some looking much like rough flints rendered transparent, others star-shaped with 

 several points, while the greater number resemble knotted clubs made of differently- 

 colored glass, and having a lovely effect under the microscope. 



