58 



THE SIMPLER METAZOA 



through the sides of the body and passes out through a 

 hole in the top. A simple sponge, called Grantia, grows 

 in salt water attached to docks or other objects submerged 

 along the seashore. On examination, it will be observed 

 that grantia is less simple than volvox. 



Figure 56. — Bath Sponge. 

 A skeleton. 



43. Structure. — Grantia is composed of three layers of 

 cells which show division of labor. The inner layer is 

 called the endoderm (en'do-derm). It consists of cells 

 provided with flagella which, by their movement, produce 

 a current of water through the central cavity. The 

 water enters through the holes in the sides (inhalent 

 pores) and is forced out through the opening at the top 

 (exhalent pore). The water contains food particles 

 which the cells of the endoderm have the power to take 

 in and digest. The food solution is passed to the other 

 cells in the sponge body by the process of osmosis. 



