FRESH-WATER SPONGE AND SOME ALLIES 277 



number of oscula. The evidence obtained through studying 

 the embryology of sponges indicates that each osculum marks 

 the position of an individual, and that the adult form results 

 from the fusion of numerous individuals originally distinct. 

 Internally, however, there is no sepa- 

 ration between individuals, their 

 chambers being continuous. 



Sycon. Some sponges that live in 

 the sea are simple ; that is, they con- 

 sist of a single individual. A sponge 

 of this kind is Sy'con (Fig. 139). The 

 free end has a single osculum. All 

 over the body elsewhere are minute 

 dermal pores leading into in current 

 canals, alternating in the substance 

 of the body-wall with radial canals. 

 Food and water entering the incur- 

 rent canals by dermal pores are 

 carried into the adjacent radial canals 

 by short canals. From the radial 

 canals the water passes into the large 

 cloaca. Waste and extra water are 

 discharged through the osculum. The spicules are composed 

 of carbonate of lime. 



The Bath-Sponge. The best known of all species of sponges 

 is, of course, the bath-sponge (Euspon'gia officina'lis). It is a 

 composite sponge of great complexity, but usually the oscula, 

 looking like chimneys, stand out so clearly that one may deter- 

 mine the number of individuals present in a mass. Varieties of 

 this sponge are found in the deep waters about the Bahama 

 Islands and in the Mediterranean Sea, especially on the coast 

 of the Turkish dominions. 



The bath-sponge grows attached to rocks in water of a few 

 fathoms' depth. Divers cut the masses at the base and later 



FIG. 139. Sycon and Spic- 

 ules. Sponge enlarged; 

 spicules much enlarged. 

 (After Grentzenberg) 



