ANIMAL LIFE 



sponges. As in the Protozoa, there are no special organs 

 for the performance of special functions. The sponge 

 feeds by creating, with its flagella, water currents which 



flow in through the many fine 

 pores of the body and out from 

 the inner body cavity through 

 the large opening at the free 

 end of the body. These cur- 

 rents of water bear fine parti- 

 cles of organic matter which 

 are taken up by the cells lining 

 the pores and body cavity, and 

 assimilated. There are no 

 special organs of digestion. 

 Each cell takes up food and 

 digests it. The water cur- 

 rents also bring air to these 

 same cells, and thus the sponge 

 breathes. Although the 

 sponge as a whole can not 

 move, does not possess the 

 power of locomotion, yet the 

 protoplasm of the cells has 

 the power of contracting, just 

 as with the Protozoa, and the 

 pores can be opened or closed 

 by this cellular movement. 

 Practically, thus, the only 

 movements the sponge can 

 . Thebody is represented make are the movements made 

 as cut in two longitudinally. The by the individual cells. 



large cells of the inner layer are the 



egg cells. Eeproduction is accom- 



plished by a process of divi- 

 sion, or by a process of conjugation and subsequent division. 

 In its simplest way multiplication takes place by a group 

 of cells separating from the body of the parent sponge, 



PIG. 18. One of the simple sponges, 

 Prophysema primordiale (after 



