A SPONGE AND A FLOKIDEA. 343 



as Algae and Fungi, also establish themselves there. Some of 

 these last have very singular habits ; it was Lieberkiihn, so far 

 as I know, who first pointed out the fact that certain algae the 

 : .-(g are invariably associated with certain species of 

 sponge, and that they grow, not on the soft portions, but on the 

 hard fibres. Other algae, again, serve as a base for the sponges 

 which cover them like an incrustation. Both of thess cases 

 might be designated as instances of parasitism if we knew thac, 

 in the former, the Florideie, living in and penetrating the fibres, 

 derived their nourishment from the sponge; or that, in tho 

 second, the algae supplied food to the sponge growing upon it. 

 But we have no certain information on these points 



FIG. 92. Sponain tartilaginra. E?per. Half the natural size. Tl.e holes in several of the 

 branches are the months or stoinata of the sponge. By far tbe greater portion of the 

 substance of the broad branches U composed of the matted filaments of an alga, flt-ridea, 



"While following up the question as to whether such pecu- 

 liarities of structure might not in fact be more common than 

 was supposed, and what the nature might be of the reciprocal 

 relations between two organisms thus associated, I unexpectedly 

 met with an object which at the first glance has all the normal 

 appearance of a highly ramified species of sponge. It seems to 

 have been so describe;! already by Esper, and I believe I am cor- 

 rect in designating the organism represented in the cut (see fig. 

 92) as the Spongia cartilaginea cf that writer. The branches, 

 which are sometimes cylindrical and sometimes flat, divide in 

 one place and reunite in another, thus forming an irregular net- 



