PLATE Il. A FRESH-WATER SPONGE. 
A. Hypothetical section of a Sfongil/a: a, superficial layer; 6, inhalent 
apertures ; ¢, ciliated chambers ; @, an exhalent aperture; e, deeper sub- 
stance of the sponge. The arrows indicate the direction of the currents. 
B. A small Sfongilia with a single exhalent aperture, seen from above: 
a, inhalent apertures; 4 ¢, ciliated chambers; d@, exhalent aperture. C. 
A ciliated chamber. D. A free-swimming ciliated embryo. 
