74 INVERTEBRATE MORPHOLOGY. 



3. Order Spiculispongise. 



The skeleton in the Spiculispongiae is occasionally entirely 

 wanting, as in the genus Ilalisarca, but usually consists of 

 siliceous spicules usually tetraxial or rod- or club-shaped, 

 sometimes interlocking with one another so as to form a firm 



Fig. 37. — A small Spongilla with only a single Osculum (from Hdxlet). 

 a = inhalent pore. c = ciliated chamber seeu through 



d = osculum. the tissues. 



skeleton. One of the members of the group is the "boring 

 sponge," Cliona, which excavates channels in and assists in 

 the disintegration of oyster-shells, frequently attacking the 

 shells of living animals and contributing to their destruction. 



4. Order Hyalospongise. 



The Hyalospongise are essentially deep-sea forms, and are 

 characterized by the possession of sis-rayed siliceous spicules 

 as skeletal elements. The spicules may become fused to- 

 gether to form a firm siliceous network having the appear- 

 ance of spun glass, as in the genus Euplectella, commonly 

 known as Venus' Flower-basket. 



Beproduction of the Pori/era. — Sexual reproduction occurs 

 probably throughout the entire group of the Sponges, the re- 



