414 



RADIATA. 



plant, the Sponge has not the slightest power of chan- 

 ging its position : "no indication of sensation has ever 

 been witnessed in them ; contact, however rude, 

 excites no movement or contraction which might 

 indicate its being perceived ; no torture has ever 

 elicited from them an intimation of suffering ; they 

 have been pinched with forceps, lacerated in all 

 directions, bored with hot irons, and attacked with 

 the most energetic chemical stimulants, without 

 shrinking, or exhibiting the remotest appearance of 

 sensibility."* Finally, we discover no semblance of 

 any cavity answering to a stomach ; nothing but 

 canals which run in all directions through the mass. 



The Common Sponge, (Spongia^ Officinalis,} is 

 seen beneath a microscope to consist of a vast num- 

 ber of very slender, transparent, horny fibres, which 

 join each other in every direction at various intervals, 

 so as to form an irregular net-work. These fibres 

 are highly elastic, returning after pressure to their 

 former position, and thus allowing liquids to pervade 

 the mass. In life, every fibre is coated with a thin 

 glairy jelly, which forms the living part of the 

 Sponge, the fibres being merely the supporting 

 skeleton. Many species, although resembling this 

 in general structure, are not at all elastic, but 

 crush on pressure, owing to the presence of numerous 

 needles or crystals of stony matter, which are scat- 

 tered among the filaments. 



Though no contraction, nor any voluntary motion, 

 can be traced in the Sponge with the closest atten- 

 * Jones. t Vvoyyos, spongos^ its ancient Greek name. 



