56 Part second. 



bean sea form the American sponge-field. After the removal of the soft 

 parts of the sponge the fishermen usually fill the skeleton with sand, so 

 as to increase its weight and thus to obtain a higher price for their goods. 

 For this reason it is necessary to rinse newly bought sponges repeatedly 

 so as to remove all foreign matter, and it is well at first to add a little 

 hydrochloric acid to the water. The sponge of commerce is found rarely 

 in the Bay of Naples. It chiefly frequents rocky coasts and coral reefs; 

 it does not live in very deep waters, where its elastic skeleton is of no 

 use, nor in cold water, where we must suppose that the material compos- 

 ing it cannot be formed. Mutilation injures K sponge but slightly; di- 

 vided with a sharp razor even the smallest fragments retain their life. 

 After a time they may die, and without doubt they suffer from the ab- 

 sence of the remainder of the cooperative body; under favourable condi- 

 tions, however, they will live and grow. Ignorant opposition of the fisher- 

 men has prevented this property from being practically used. 



POLYPES (ANTHOZOA). 



If it be difficult tho the lay mind to apply the term Sponge to or- 

 ganisms , which in a living condition are not at all of a spongy nature, 

 it wilt be found equally difficult to picture as Corals anything else than 

 the beautiful red and white branches which are displayed as ornaments 

 on writing-desks and chimney-pieces. And yet these branches are not 

 really the animals themselves , but only the framework which they have 

 built themselves, and in which they live imbedded, in hundreds or thou- 

 sands, side by side or one above the other. 



Of the polypes, tha animals which build up the corals, the best con- 

 ception may be gained by examining those kinds which are considered 

 the chief attractions of the northern Aquaria, namely the 



SEA-ANEMONES (ACTINIA). 



These animals exhibit a cylindrical body, attached by an adhesive 

 disk to some fixed object and bearing at its free end numerous very mo- 

 bile tentacles. These encircle an aperture , which serves both as mouth 

 and as anus (Fig. 160); it leads into a capacious stomach in which the 

 food is digested. The soft and apparently unprotected polype is really 

 very well armed. Many parts of the body , but especially the tentacles 

 which serve to catch its prey , are provided wiht numerous microscopic 

 vesicles, the so-called stinging-cells, each containing an acid liquid and a 

 spirally coiled thread. When the animal comes in contact with its enemies 

 or its prey thousands of these stinging-cells burst , ejecting forcibly the 

 long filament ; this bears a sharp point and is often barbed , while the 

 noxious liquid in its core renders the tiny wound it makes sufficiently 

 poisonous to benumb or even kill. The ejection may be compared to blow- 

 ing out the fingers of a glove when they are tucked in, The Anemo- 



