308 SEA-ANEMONES, ZOOPHYTES, ETC. 



existence since perhaps before the distant Laurentian 

 epoch of which geology speaks. They have expe- 

 rienced all the changes which we know the ocean 

 beds must have experienced have repeatedly wit- 

 nessed the conversion of continent into sea, and 



Fig. 238. 



" Crumb-of-bread " Sponge (Halichondria panicea). 



ocean floor into dry land and even mountain chain. 

 The mineral remains of some of the ancestors of 

 living forms have taken an active part in the building 

 up of rock masses of every geological period. We 

 cannot wonder, therefore, that the number of species 

 of these early and unpretending forms of life should 



