206 



THE BIOLOGY OF MARINE ANIMALS 



carea), the choanocytes lie in elongated radial canals lying at right angles 

 to the internal surface. Water currents enter incurrent canals via ostia, 

 pass through prosopyles (pores) into the flagellated chambers and from 

 thence into the central cavity or paragaster, which opens to the exterior 



Epidermis 

 / 



Fig. 



Flagellated 

 chamber 



5.2. Section through the Body Wall of a Calcareous 

 Sponge Leuconia aspera. (From Vosmaer, 1880.) 



through an osculum. Most sponges show a leuconoid type of structure in 

 which the choanocytes are restricted to small chambers which communi- 

 cate with the paragaster by exhalant canals. 



The hydraulics of this system have been investigated in Leuconia, a 

 calcareous sponge of leuconoid type, from which the following measure- 

 ments were obtained. 



The total pressure involved in this flow varied from 1 to 3 mm of water. 



It appears from these calculations that the maximal surface area and 

 slowest rate of flow are found in the flagellated chambers, especially at 

 the surface of the choanocytes, and this will permit maximal opportunity 



