OF THE NATURE OF SPONGES. 57 



MM. Audouin and Milne-Edwards, after an attentive 

 study of the sponges indigenous to the shores of France, 

 confirm the exactness of Dr Grant's statements relative to 

 these singular productions,* which certainly possess an ani- 

 mal life — " vivent d' une vie tout animal," — but to which 

 the anatomist may be tempted to refuse animality, since 

 he cannot distinguish in them any organ by which it is cha- 

 racterized. Fixed to rocks at great depths they found some 

 remarkable bodies, belonging to this tribe of beings, whose 

 surface was entirely covered with a thick siliceous crust. 

 Their texture is composed of spicula of crystallized silex, 

 varying in form according to the species, and of an organic 

 substance which appears to be no other than a confused 

 mass of globules of extreme littleness. The form of the 

 elements of the crust varies also ; — sometimes these are 

 spicula, at other times ovoid granules of siliceous matter. 

 In most of the species there are two kinds of openings in 

 the crust in communication with the interior canals, — the 

 lesser which give entrance to the water around them, — 

 and others, considerably larger, by wliich that water es- 

 capes. These productions, allied at once to organic 

 and unorganized matter, — " qui tiennent a la fois de la 

 nature organique et inerte," — appear to belong to the 

 Geodise, and to constitute a genus allied to the sponge. 



In reference to the non-irritability of the sponges, pro- 

 perly so called, Audouin and Milne-Edwards agree with 

 Dr Grant ; but they found indications of irritability in the 

 Tethya, — whose structure approaches that of the semi- 

 spongoid, semi-siliceous bodies just mentioned. When 

 the Tethya is placed in a vessel of sea-water, and left, for 



* L;iniaick"s Anim. s. Veil, -ide edit. li. p. lOo- 



