PHYLUM PORIFERA 83 



is intracellular the cavity is not a true digestive cavity and there- 

 fore not a stomach. Opening and closing of the pores leading 

 into this flagellated chamber are under control of the animal. 

 When the pores are open, the action of the flagella causes water 

 currents bearing food material to pass through the flagellated 

 chamber and out through the osculum. During this passage, 

 food is removed from the water and ingested by the cells. Leu- 

 cosolenia and Olynthus are examples of this simplest type of 

 sponge organization. 



The Sycon (Fig. 49 B) differs from the foregoing chiefly in the 

 fact that the central cavity is lined with pavement epithelium 

 and the flagellated cells have withdrawn to small radial chambers 

 or ampullae embedded in the thickened wall. The central 

 cavity is now a distinct cloaca with which each ampulla communi- 

 cates by means of a small opening called the apopyle. As the 

 name implies, the radial chambers are arranged radially about 

 the cloaca. Alternating with the radial chambers are the incur- 

 rent canals which pass from the exterior inward toward, but not 

 into, the cloaca. Minute openings, the prosopyles, communi- 

 cate between the incurrent canals and the adjacent ampullae, 

 thus allowing water currents bearing food material to pass 

 through the radial chambers, into the cloaca and out through the 

 osculum. Grantia and Sycon are two typical genera whose 

 representatives are built upon the Sycon plan. 



As they acquire greater bulk, some sponges reach a size wherein 

 direct communication between the ampullae and the exterior 

 and cloacal surfaces is no longer possible. Intricately branched 

 incurrent and excurrent canals establish these surface relations 

 for the deeply embedded ampullae (Fig. 49 C). Sponges of this 

 character are of the Leucon type and are typified by such genera 

 as Leucilla and Oscarella. 



Physiology of Sponges. — Regardless of the type, all sponges 

 are fundamentally alike in their methods of securing food. 

 Movements of the flagella in the flagellated chambers produce 

 water currents through the canal system of the sponge. Food 

 particles entering the flagellated chambers are ingested by the 

 cells, and the process of digestion is wholly intracellular. From 

 the incurrent streams of water the sponge derives its nourishment 

 and its oxygen for respiration while the same water stream as 

 it leaves the body by way of the osculum carries the metabolic 

 wastes. 



