THE HIGHER ORGANISMS 



121 



terval usually without cells, but sometimes containing 

 cells of amoeboid character that have crawled in between 

 the other cells. This space with whatever cells it con- 

 tains is called the mesenchyme. In such a simple organ- 

 ism, the chief office of the outer cells of the body is to pro- 

 tect it by forming an elementary or primitive cuticle. 

 The office of the cells of the inner layer is to dissolve nutri- 



FIG. 42. Diagram of simple type of sponge, c, cloaca; ch, chambers, lined 

 with flagellate entoderm; e.p, external pores; i.p, internal pores; mes, mesen- 

 chyma; o, osculum; r.c, radiating canals; ec, ectoderm; en, entoderm. In the 

 adult sponge the canals and flagellate chambers become much more complex 

 than figured here. (Galloway.) 



tious particles brought into the body cavity by the ten- 

 tacles. Through their action the fluid contained in the 

 body cavity becomes nutritious enough to enable the 

 cells to live by absorbing it, the inner cells passing it to 

 their next neighbors of the outer layer, or permitting it 

 to transfuse into the mesenchyme from which it reaches 

 them. 



