POBIFEIiA. 



219 







remain in the mesoderm, and there undergo their development. It 

 is only later that the 

 ciliated embryos or 

 larvae fall into the 

 canal system, pass 

 out, and attach 

 themselves, to de- 

 velop into a young 

 sponge. 



The embryonic de- 

 velopment among the 

 calcareous sponges is 



most accurately FIG. 165. Ewpongia officinalis adriaf.ica, with, a number of 

 ,. oscula, O (after Fr. E. Schulze). 



known for the 



Sycvnidce from the investigations of Fr. Schulze and Barrois. 



a, 





FIG. 166. Development of Si/con rapTianus (after Fr. E. Sclmlze). a, Uipe ovum, b, Stage 

 with four segmentation cells, c, Stage of segmentation with sixteen cells, d, Blostosphero 

 with large dark granular cells at the open pole, c, Free-swimming larva, ouc-half of the 

 body (entodermal) being formed of long ciliated cella, tho other (ectoderuiu.!) of large 

 granular cells. 



