FIGS. 1—6. — DIAGRAMS ILLUSTRATING CANAL SYSTEMS IN DIFFERENT TYPES OF SPONGES (after Schuke). 

 L Ascon type ; 2-5. Variations of Sycon type ; 6. Rhagon type ; ect., ectoderm of exterior; 

 ect ' , ectoderm of atrial cavity ; mes., mesoderm ; end., endoderm ; osc, osculum; atr., atrial cavity 

 or cloaca ; cho., choanocyte layer ; cc., flagellate chambers; /., pores; prp., prosopyles ; apy., 

 apopyles ; ink., inhalent cavities; exh., exhalent cavities. 



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