SPONGES 



(Fig. 83, D) into the gastral chamber (Fig. 83, E). Here it 

 mixes with water from other canals and finally goes out of 

 the osculum (Fig. 83, F), carrying waste matters with it. 

 In a young sponge the oscula are at the tops of chimney-like 

 elevations, and with a lens, waste particles can be seen coming 

 out of these "chimneys" along with the water (Fig. 85). 

 Sponges are wholly dependent upon currents of water for 

 bringing them food and carrying away waste; they may be 

 fed or smothered to death, depending upon whether currents 

 bring clean water supplied with food or water heavy with 

 silt. Sponges cannot move from place to place but their 

 gemmules or winter buds (Fig, 84) have been carried about 

 by birds and by currents of water ; and sponges have thus been 

 widely distributed through lakes and streams. 



Habitat. — Sponges can live only in clean water. They 

 grow upon water-soaked logs sometimes in large masses, on 

 the leaves of submerged plants, and often with bryozoans 

 on the undersides of stones in riffly brooks. It is not strange 

 that they are abundant on sluiceways and pipes at the 

 outlets of reservoirs, where the water is free from mud and 

 rich in microscopic organisms. Water-pipes are often lined 

 with rough coatings of sponge a quarter of an inch or more 

 thick which hinder the flow of the water and sometimes totally 

 clog the pipes. Occasionally the sponge decays and throws 

 out impurities, giving the well-known "swamp taste" to 

 the water. Sponges and bryozoans are both called "pipe 

 moss" by sanitary engineers. When the Metropolitan Water 

 Works were installed in Boston, an old sixteen-inch pipe was 

 opened which had been laid ten years before. Scattered over 

 the usual coating of rust were numerous patches of sponge 

 as large as the palm of one's hand. These were all growing 

 lustily without any light at all since th&» unfiltered reservoir 

 water was clean but full of food. 



Sponges often live where they are flooded with sunlight 

 and then they are colored green by the chlorophyll of minute 



107 



