THE PORIFERA. 



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Fig. 12. — A. Hypothetical section of a SpongiUa : a. superficial layer; b. inhalent 

 apertures ; c. ciliated chambers ; d, an exhalent aperture ; e, deeper substance 

 ofthe SDonsre. The arrows indicate the direction of the currents. B. A small Spnn- 

 gVfa with a single exhalent aperture, seen from above (after Lieberkiihn): a. in- 

 halent apertures ; c. ciliated chambers ; d. exhalent aperture. C. A ciliated 

 chamber. D. A free-swimming ciliated embryo. 



8 



