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TEXTBOOK OF ZOOLOGY 



and other less conspicuous spicules are distributed over the body. 

 The ostia are the incurrent pores through which water is taken into 

 the body. They are quite evenly distributed over the wall. A dermal 

 epithelium covers the outer surface of the animal. 



Internal Anatomy 



Internally there is a large central or gastral cavity which is simply 

 a water cavity and is not comparable to a stomach or enteron. In 



Dctfnal 



EpiiKctium 



•1 



k«l>M«n 



FlaftlUitd Oitmbc 

 (Radul Canal) \ 



10% 



4^ 11... cu.- 

 I ■■■"« 



DiAfftftm of Akod Sponge 



S-' . : ■ : S , Caiiral Co.ihcl.um 



. InkaltAI Canal 



Charr.bcr 



Stereogram to illuatntc ample Leucen Sponge 



Dermal Oatta 



^Subdarmal Cavity 



Ch^lcnf Cnal 



FUstlUied Cham^r 



StetcogrKiT) to illustiate Sycon Sponge 



Diagram L, S, of rSagon (Icucon) type of canal 3truc:ure such «9 occurs 

 in the Demospongiae 



Fig. 52. — Structure of different types of sponges, shown diagrammaCcally. 

 (Courtesy Pacific Biological Laboratories.) 



more complex sponges there may be several or even many such 

 cavities, each one opening distally by an osculum. Communicating 

 with and radiating from this cavity is a set of radial canals. They 

 join the cavity through small pores called apopyles and extend nearly 

 to the outer surface of the wall where they end blindly. Lying be- 

 tween these and extending inward from the ostia are the incurrent 

 canals. They connect with the radial canals by rather numerous 

 apertures called prosopyles. This canal system not only serves to 



