ZOOLOGY. 



(I. ASS (H THE SPONGIARIA. 



623. The sponges (Fig. 168) and the other bodies of an ana- 

 logous structure, only present the more prominent eharac1iT> <>t' 

 ammality during the early period of their life, and reM-ml>lf 

 later rather unformed vegetables than ordinary animals. At 

 the time of birth, these singular beings sufficiently resemble 

 certain infusoria; their body is oval, and provided all over 

 with vibratile cilia, by means of which they swim in the 

 waters ; in this respect they bear a resemblance to the larva 1 

 of different polyps at the moment when they leave the egg ; 

 but soon the young sponges attach themselves to some 

 foreign body, become almost immovable, give no longer any 

 signs of sensibility or of contractility, and as they grow, be- 

 come completely deformed. The gelatinous substance of 

 their bodies becomes pierced with holes and canals, traversed 

 unceasingly by the waters, and there is developed in their in- 

 terior a number of horny filaments and spiculae, sometimes 

 calcareous, sometimes siliceous, which, disposed in cross bun- 

 dles, constitute a kind of solid framework. Finally, at cer- 

 tain epochs of the year there are developed in the substance 

 of these shapeless masses, ovoid or spherical corpuscles, which 

 fall into the canals already mentioned, and which, drawn out- 

 wards by the current by which the sponge is constantly tra- 

 versed, constitute species of larva? or reproductive bodies, en- 

 dowed with the locomotive faculty mentioned above. 



A great number of these sponges, or spongiaria, are known 

 to naturalists ; most of them belong to the seas of warm 

 regions, but several live on the rocks of our coast. Those 

 used so abundantly in domestic economy are distinguished by 

 the purely horny nature and by the elasticity of the filaments 

 of which their solid framework is composed ; one of the 

 species, the common sponge, is found in great abundant - v in 

 the Mediterranean ; another, called usual, belongs to the 

 American seas. These bodies are the object of an important 

 commerce, and to prepare them for the uses to which they 

 are destined it is sufficient to wash them well, so as to detach 

 from their horny skeleton the animal matter with which 

 it is naturally covered. 



