CHAPTER XXVI 



THE BATH SPONGE AND SOME ALLIES: PORIFERA 



The unending shapes of plants, the rainbow's varied hues, 

 All these the lowly sponge on ocean's bed renews. 



Habitat and Form. Sponges live in the ocean both in shal- 

 low and in deep waters, and members of one family live in 

 fresh water. Some kinds have no characteristic shape of 

 their own, for they merely form crusts over rocks or other 

 objects (Fig. 148). Some have a definite cup-like shape, 

 while others grow as branching structures or are solid 

 rounded masses. Sponges are animals of a very low type of 

 organization. They have no organs of locomotion. In fact 

 they have no highly specialized organs of any sort. As a 

 consequence in general appearance they rather closely re- 

 semble plants. 



Structure. One of the most characteristic features of a 

 sponge is the practically solid body penetrated by numerous 

 openings (Figs. 148, 149) which lead into an internal sys- 

 tem of spaces or tubes. There are no true body cavities. 

 The systems of openings and tubes penetrating the body 

 are simply channels for the surrounding water to pass 

 through (Fig. 149). In passing through the body, the water 

 brings food to the tissues. The form of the body is largely 

 due to supporting or skeletal material. In many of the 

 sponges the skeleton is made up of spicules of lime or of a 

 glass-like (silicious) material. Another type of framework, 

 or skeleton, in sponges is a soft fibrous material arranged in 

 the form of a network running all through the body. The 

 sponges used in house-cleaning and usually sold under the 



283 



