1 66 Dzvellers of the Scci and Shore 



copper. And then there Is its paler cousin (C arhiis- 

 ciila)y standing about six inches high, whose delicate 

 and finer textured branches of tawny gray grow more 

 slender but in greater profusion. Some sponges re- 

 semble crumbs of bread; others spread themselves in 

 irregular golden masses over the fronds of seaweeds 

 or the surfaces of stones. These latter generally first 

 find their way here as fragments. Soon or late, how- 

 ever, some of these fragments drift into contact and 

 coalesce, forming a single but larger and perfect unit. 

 Still, of all the immigrants, the boring sponge {Cliona 

 stilphiirea) has the most striking habits. It is a light 

 cream yellow in color and usually grows on the dead 

 shells of the oyster and hard clam, though it some- 

 times settles on living shells to the great irritation 

 of the animal within. It honeycombs these shells 

 with galleries by absorption, wherein it establishes it- 

 self, showing only its wartlike prominences through 

 little perforations about one eighth of an inch in diam- 

 eter that riddle the surface of the valves. In time the 

 dead shell is completely disintegrated by the work of 

 this persistent borer, but the living mollusk, although 

 hard put to prevent this disaster to itself, manages 

 to delay if not effectually resist these encroachments 

 by the constant secretion of new lime over the parts 

 that are penetrated by the sponge. 



But the sponge population of the tide pool is by no 

 means composed entirely of immigrants. A community 

 long established herein also holds its own. The bril- 

 liant orange-red incrusting sponge {Microcioua pro- 

 lifcra), spreading itself in a velvety, tangled mass over 

 shells and stones, is a conspicuous example. Less color- 



