PORIFERA 



233 



entoderm, and a middle gelatinous connective-tissue matrix 

 in which are embedded branched connective- tissue cells, 

 calcareous or sihcious spicules, primitive muscle cells and repro- 

 ductive cells. Through the walls of the si)onge numerous fine 

 pores or slender canals penetrate from the exterior to the 

 central larger canal or cloaca. In the simpler sponges the 



Fig. 132. — A Niaxon sponge (Phcroncma?). Philippine Islands. X 1/2. 



surface of the cloaca is lined with the colhircd llagellalc cells. 

 These have a marked resemblance to the protozoan C'lioano- 

 flagellata and are not found in any other metazoa. llie 

 lashing of the fiagella creates a current in the water which tlows 

 inward at the pores and outward at the osculum, the large open- 

 ing of the cloaca. The fiagella and collars together serve for 



