OS 



FU -Jit. Diagram of sponge. />, Fig-. 29a. A longitudinal section through a 

 one of the numerous pores or mouths; simple calcareous sponge, showing the simple 

 c. a ci Mated chamber or pocket; os, central cavity; b, showing a single osculuru at 

 osculum. the top, and the many mouths over the surface. 



g'c 



Fig. 306. Development of a sponge (Sycon raphanus). A, ripe egg; B, stage with 

 foursegmentatiou-cells; C, morula stage, with sixteen cells; D, blastosphere(blastula), 

 with large dark granular cells (</c) at the open pole; E. 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. J 



