532 SEPARATION AND MOUNTING OF SPONGE-SPICULES. 



Skeletons to their fleshy substance, can he demonstrated. — In order 

 to ohtain the Spicules in an isolated condition, however, the animal 

 matter must be got-rid-of, either by incineration, or by chemical 

 reagents. The latter method is preferable, as it is difficult to free 

 the mineral residue from carbonaceous particles by heat alone. If 

 (as is commonly the case) the spicules are Siliceous, the Sponge 

 may be treated with strong nitric or nitro-muriatic acid, until its 

 animal substance is dissolved away ; if, on the other hand, they be 

 Calcareous, a strong solution of potass must be employed instead of 

 the acid. The operation is more rapidly accomplished by the aid 

 of heat ; but if the saving of time be not of importance, it is pre- 

 ferable on several accounts to dispense with it. The spicules, when 

 obtained in a separate state, should be mounted in Canada balsam. 

 — Sponge-tissue may often be distinctly recognized in sections of 

 Agate, Chalcedony, and other Siliceous accretions, as will hereafter 

 be stated in more detail (Chap. xix.). 





