Ill 



Fig. 12.—A. Hypothetical section of a Sponqilla: a. superficial layer; b, inhalant 

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

 ot the sponge. The arrows indicate the direction of the currents. B. A small Snon- 

 giua 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 Iree-swimming ciliated embryo. 

 8 



