322 APPLIED BIOLOGY 



pass through to the inner canal and thence into the central 

 cavity. The inner canal is lined with numerous cells, each 

 of which has a long, whip-like structure (flagellum) ; and it is 

 the lashing of all the flagella which causes water to flow in 

 through the pores. 



Structure of a Simple Sponge. (D) Grantia is the name of a small 

 marine sponge found attached to stones, piles of wharves, etc. Schools 

 far from the sea must use specimens preserved in alcohol. While 

 observing, keep the specimens covered with alcohol or water in 

 watch-glasses, or in small bottles, one specimen in each bottle. Have 

 some specimens entire, and some split longitudinally. Use a hand- 

 lens, and identify all structures, except cells, mentioned above. 

 Some cross sections, cut with a razor, should be demonstrated to show 

 the spicules which form the skeleton. That these are calcareous 

 spicules can be shown by pouring some acid on them. The fleshy 

 substance (i.e., the cells) can be cleaned away by boiling a Grantia 

 sponge in a strong solution of caustic potash. 



The feeding of a sponge-animal is similar to that of a para- 

 mecium. The cells with flagella, in the inner canals, are 

 able to take in and digest food particles brought by the in- 

 coming currents of water. Indigestible particles are carried 

 out of the central cavity by currents of water. Those cells 

 which are not fitted to take in and digest food may obtain 

 digested food by osmosis from the other cells. Here is a 

 simple step in physiological division of labor; the outside 

 cells are the protective covering of the body, and some of the 

 inner cells digest food. 



The outer cells are collectively known as the ectoderm 

 (meaning outer skin), while the inner layer of cells which 

 line the inner canals and central cavity and do the digesting 

 constitute the endoderm (meaning inner skin). 



Reproduction. Sponges reproduce by outgrowths or buds 

 from the older animals, and when the animals thus formed 

 remain together colonies are formed. Figure 96 shows 

 a colony of three individuals formed by two buds on the 



