378 The Animal Kingdom 



123). In this sponge, an infolding of the walls adds extra chambers and 

 necessitates additional canals for the circulation of water. An incurrent 

 canal is located between the outer folds of the sponge wall. Water en- 

 ters this canal through dermal ostia or pores. From this incurrent 

 canal, the water passes into the choanocyte-lined radial canal by means 



Fig. 122. — Canal systems of sponges. 1, Mesenchyme; 2, choanocyte layer; 3, 

 incurrent pore; 4, spongocoel; 5, osculum; 6, incvirrent canal; 7, prosopyle; 8, radial 

 canal; 9, dermal pore; 10, apopyle; 11, flagellated chamber; 12, excurrent channel. 



eAse 



.MESENCHYME 



B 



inqubren t canal ___^ ,^j_ _ 

 """"" naniAi CAN> 



RADIAL CANAL 



Fig. 123. — Scypha. A, External view; B, portion of body wall; 

 C, amphiblastula; D, choanocyte or collar cell. 



