142 TOILERS IN THE SEA. 



may apply that term to them generally, whereas 

 some are straight and others curved, some with a 

 head like a pin, and others sharp at both ends, some 

 rough and others smooth. Then again there are 

 rayed spicules, some with three rays, some with four 

 rays, like a cross, and some with many rays. These 

 are sharp at the ends, or blunt, or spiny. Some again 

 are shaped like hooks, or forks, or tridents, simple or 

 complex. Others again resemble anchors, or wheels, 

 or stars, or spiny spheres ; in fact, to enumerate all 

 the forms would be to produce an uninteresting cata- 

 logue, which a few figures would perhaps obviate. 

 Suffice it to say that almost any typical form has 

 numerous modifications. 



These flinty spicules, which are peculiar to sponges, 

 are practically indestructible (^fig. 16), and, from the 

 position in which they are found, it is indisputable 

 that sponges must have flourished in the ocean very 

 many thousands of years ago. Dr. Bowerbank was 

 of opinion that almost every flint stone was once a 

 sponge, or had a sponge for its nidus. A writer on 

 the " Spongeous Origin of Flints " l says, " If a thin 

 chip or section of flint is submitted to microscopic 

 examinations, sponge spicules in more or less 



1 " On the Spongeous Origin of Flints," by F. Kitton, in 

 Transactions of Norfolk and Norwich Naturalist^ Society r , 

 (1871-2), p. 51. 



