meS 



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



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

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

 or cloaca ; f/?o., choanocyte layer ; cc, flagellate chambers; /., pores; /r/., prosopyles ; apy-, 

 apopyles ; inh., inhalent cavities; exh., exlialent cavities. 

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