Fig. 29.—Diagram of sponge. p, Fig. 29a.—A longitudinal section through a 
one of the numerous pores or mouths; simple calcareous sponge, showing the simple 
c, a ciliated chamber or pocket; 0s, central cavity; b, showing a single osculum at 
osculum the top, and the many mouths over the surface. 
Fig. 80b.—Development of a sponge (Sycon raphanus), A, ripe egg; B, stage with 
four segmentation-cells; C, morula stage, with sixteen cells; D, blastosphere (blastula), 
with large dark granular cells (gc) at the open pole; EH, free-swimming blastula, one 
half of the body (endodermal) being formed of long ciliated cells, the other (ectoder- 
mal) of large granular cells. All highly magnified.—After Schultze. 
[To face page 44.] 
