PORIFERA 



231 



They are often branched, especially the cylindrical ones and 

 the more massive forms may become very irregular in shape 

 through the development of new parts by irregular Ijudding. 

 Some are very delicate and fragile while others are very firm, 

 even stony. The color is as variable as the form; they arc often 



Fig. 130.— a large cup-shaped sponge (Poterion?) from the Philippine Islands. 



X 1/8. 



a dull gray but highly colored species are very common. Or- 

 ange, sulphur yellow, violet, purple and green sponges often 

 give color variety to the sea bottom. The fresh-water Spongilla 

 is usually green; the color in this case being due to the presence 



