112 
THE OCEAN WORLD. 
riddled with air-cells. This tissue is formed of delicate flexible fibred 
uniting in all directions by anastomose, hut presenting numerous por eS) 
which are formed by what is termed osculation, haying irregular condu^ 1 
which connect them. In this tissue certain very small solid bo<b eS 
are discovered, named spiculse. The spiculte are siliceous or calcare° n? 
in their nature, varying according to the species, and sometimes varyb 1 ^ 
Fig. 39. Spoiigiu, half the natural size, attached to Ut> rueky bed. 
