SPONGES, FLAT WORMS, AND ROUND WORMS 145 



animal a ciliated appearance. The body wall is perforated by 

 numerous incur rent pores. This characteristic has suggested the 

 name Porifera (Lat. poms, a pore, and ferre, to bear) to mem- 

 bers of this phylum. 



Structure. A specimen of Grantia split longitudinally (Fig. 

 70) shows the body to be a hollow sac, one large central cavity, 

 the cloaca, being pres- 

 ent. The body wall is 

 honeycombed by a 

 great many canals; 

 some of these, the 

 radial canals, open to 

 the cloacal cavity 

 through minute pores, 

 the apopyles, and end 

 blindly near the outer 

 surface; others, the in- 

 current canals, open to 

 the outside through 

 small incurrent pores 

 or ostia, and end 

 blindly near the inner 

 surface of the body 

 wall; still other canals, 

 the prosopyles, even 

 smaller than those al- 

 ready noted, connect 

 the radial with the in- 

 current canal. Figure 



FIG. 70. Longitudinal section of a 



sponge, ip., incurrent pores; o., oscu- 

 lum. (From Parker and Haswell.) 



70 shows in longitudinal section the cloacal cavity of a simple 

 sponge, at the bottom of which are the openings of the radial 

 canals; the body wall is seen to be crowded with both radial 

 and incurrent canals, which have been cut lengthwise. The 

 relations of the various canals to one another are shown in 

 Figure 75; here the arrows indicate the direction of the current 

 L 





