SPONGES. 161 



SUMMARY OF IMPORTANT FACTS. 



1. Sponges have one or more digestive cavities (ampullae) 

 connected with the external world by numerous incurrent 

 pores and one or more excurrent oscula. 



2. Water flows through these pores and the connecting 

 canals , bringing nourishment to the animal; waste is car- 

 ried away by the osculum. 



3. Sponges reproduce by eggs and by budding. There 

 is no alternation of generations. 



4. A skeleton is usually present; according to its nature 

 sponges are divided into Calcarea and Silicea. 



