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THE HALICHONDRIA. 



IN the genus Grantia, which is well known to marine zoologists as having furnished 

 valuable information respecting the nutriment and reproduction of the Sponges, no 

 horny network can be found, but its place is supplied by the singular form of the spiculae, 

 which are composed of three long-pointed spines arranged so as to form a star of three 

 rays. These rays, on account of their shape, form an entangled mass, and answer the 

 purpose of the ordinary horny framework. The new species shown in the illustration 

 inhabits the East Indies. 



There are several British species of the genus Grantia. Some of them are hollow, 

 and stand out with tolerable boldness from the objects on which they are set, while 

 others are always found as whitish incrustations upon stones and other massive sub- 

 stances. Their structure is tolerably firm, and, on account of the absence of the horny 

 framework, is not so elastic as are the generality of the Sponge tribe ; and the texture 

 is very close, but still porous. With a microscope of tolerably high power, magnifying 

 from two to three hundred diameters, the layer of spiculae can be readily made out, in- 



HalichAndria palm&ta. 



terlacing with each other in wonderful profusion, and so completely intermixed that a 

 single spicula is scarcely ever separable from the general mass. 



The shape of the species belonging to this genus is extremely variable, but in all the 

 structure is remarkably simple, the wall being extremely thin, so that the ramifying 

 canals are not needed, and the water is merely absorbed through the minute pores of 

 the wall and expelled through the large orifice which forms the mouth of the sac. If 

 the spiculae of this or other Sponges be wanted in a separate state, the animal matter 

 can be removed by heat ; but a better, though slower process, is to immerse the speci- 

 men in strong nitric acid or liquor potassae, according to the flinty or chalky nature of 

 the spicules. When separated they may be mounted in two ways, namely, as dry and 

 opaque objects, or in Canada balsam. 



WE must now briefly examine a rather important genus of Sponges, which has many 

 representatives in the British seas. It is a very extensive genus, and its members are 

 variously shaped, all, however, agreeing in those salient points on which the group has 

 been founded. They are all spongy, elastic, not slimy, and with a very porous surface. 



