THE PORIFERA. 



Ill 



'^^w//;iiiffi\\uw*^' 



Fig. 12.— a. Hypothetical Pection of a SpongiUa: a. superficial layer; b, inhnlent 

 apertures; c, ciliated chambers ; rf, an exhalent aperture; e, deeper siibstance 

 of the spousje. The arrows indicate the direction of the currents. B. .\ small Spon- 

 giUa with a sinijle exhalent aperture, seen from above (after Lieberkulin) : a. in- 

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

 chamber. D. A. Iree-swimming ciliated embryo. 



