56 SPONGES. 



animal parts which pi'oduce it. But aa all kinds of sponges do not 

 produce an almost imperishable skeletal structure like that of the 

 Oflicinal Sponge it is desirable to state that (using the term " Spongida " 

 for the whole class) it may be divided into eight orders, as follows : — 



Ord. I., Carnosa. — These sponges have no imperishable skeleton or 

 organ of support, and substantially present to the unassisted eye nothing 

 but a gelatinous or semi-cartilaginous mass, charged or not with spicules 

 according to the family to which they belong. 



Ord. II., Ceratina. — In these there in a comparatively imperishable 

 skeleton, composed of horny fibre cored throughout by an axial canal, 

 which, in the fresh state, is filled with a soft granular substance that, on 

 di-ying, is replaced by a hollow cavity. 



Ord. III., PsAMMONEMATA. — Here there is not only a horny, fibrous 

 skeleton, with a more or less granular axis in the fibre, but this for the 

 most part is filled with/o)Y/r/» material, such as particles of sand, frag- 

 ments of sponge-spicules, and the like minute bodies, drawn in from 

 the exterior, and, therefore, arranged in position by the sponge previous 

 to its becoming the axis of the hoi'uy filament. 



Ord. IV., Rhaphidonemata. — In these, the horny, fibrous skeleton is 

 well developed and very x^esilient, but the fibre is axiated by spicules, 

 (siliceous bodies of different kinds varying in form with the species,) 

 produced by the sponge itself, and therefore not foreign ; hence might be 

 termed " proper." 



Ord. v., Echinonemata. — Here we have only to add to the foregoing 

 an external set of proper spicules, which project vertically from the 

 surface of the fibre, like prickles on a hedgehog's back. 



Ord. VI., HoLORHAPHiDOTA.— We lose the hornij element here, 

 and, for the most part, the fibre is made up of proper spicules, held 

 together by the slightest quantity of sarcode ; or they may be dispersed 

 throughout an areolated sarcode, which, in the dried state, looks like 

 crum of bread. 



Ord. Vn., Hexactinellida. — Again we have fibre here without the 

 horny element, but the fibre is vitreous, so that it is like spun-glass, 

 while all the spicules, of whatever form they may be, axiate its interior. 

 The spicules, too, are all developed upon a hexradiate type, (hence the 

 name of the order,) that is, the central point of the canal, (which 

 traverses all siliceous spicules, and upon whose extension in different 

 directions their ultimate forms respectively depend,) presents six buds or 

 lines radiating from each other at equal angles, so that, if surrounded by 

 a glass cube, they would meet the centre of each side respectively ; or 

 there may be no fibre at all, and the areolated sarcode when dry, like 

 "crum of bread," as in many of the Holoruaphidota, where the spicules 

 also are dispersed throughout the mass without any apparent 

 regularity. 



Ord. VIII., Calcarea. — -Here all the spicules, instead of being 

 siliceous, are, minerally, composed of carbonate of lime. 



