SUB-KINGDOM II. POBIFERA. 



Orders. 



1. Myxospongiffi. 6. Hexactinellidae. 



2. Ceratospongiae. 7. Octactinellidse. 



3. Monactinellidae. 8. Heteractinellidse. 



4. Tetractinellidae. 9. Calcispongiae. 



5. Lithistidae. 



THE Porifera includes the Sponges. They are dis- 

 tinguished from the Protozoans by the body being always 

 multicellular, by the cells being arranged in definite 

 layers, and by the occurrence of sexual reproduction. 



In a simple sponge the body has the form of a hollow 

 sac open at the upper end, and in nearly all cases attached 

 to the sea-bottom or to a foreign object, by the lower. 



FIG. 5. Diagram of the Structure of a simple Sponge, one canal only 

 shown, os, osculum; p, pores; i, incurrent or inhalent canal; 

 c, globular chamber; e, excurrent or exhalent canal; o, ostium. 



