74 



IN VERTEBRA TE MORPUOLOO 7. 



3. Order Spiculispongise. 



The skeleton in the Spiculispongise is occasionally entirely 

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

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

 sometimes interlocking with one another so as to form a firm 



^f 



^\ 



^^^fL^^W^ffi^^ ' 

 c l^^f^xV: ^/w.if-^%'--i^^-< 



FIG. 37. A SMALL Spongilla WITH ONLY A SINGLE OSCULXJM (from HUXLEY). 



a inhalant 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. 



1. Order Hyalospongiee. 



The Hyalospongise are essentially deep-sea forms, and are 

 characterized by the possession of six-rayed siliceous spicules 

 as skeletal elements. The spicules m&y become fused to- 

 gether to form a firm siliceous network having the appear- 

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

 known as Venus' Flower-basket. 



Reproduction of the Porifera. Sexual reproduction occurs 

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



