HALF AN HOUR WITH SPONGES. 



61 



with a yellowish substance. Singularly enough, 

 these perforations are the work of a sponge, called 



Fig. 22. 



Portion of Oyster-shell perforated by Clione. 

 Fig. 23. 



Section of Oyster-shell perforated by Clione. 



Clione, of which the yellow substance is part. How 

 it excavates the holes and cavities is a mystery, but 

 it seems to have the power of dissolving away the 



