Reactions of Sponges 3 



in color and, though sometimes simply massive in habit, it gener- 

 ally rises in finger-like processes from, an incrusting base (Fig. i). 

 It is found near low-water level, and some colonies are so situated 

 that at the spring tides they may be continuously exposed to the 

 air for as long as four hours. As a rule the massive form is charac- 

 teristic of those colonies which from time to time are exposed to 

 the air; the long-fingered type is limited almost exclusively to such 

 as are never uncovered by the sea even at the lowest tides. A 

 Stylotella grows on the upper surfaces of stones, etc.. in shallow 



Fig. I. Side view of a colony of Stylotella heliophila \\'ilson, about natural size. From a photo- 

 graph taken by Dr. H. V. Wilson. 



water, it is often in strong sunlight for the greater part of the day 

 and in fact when uncovered by the tide it may also be exposed to 

 the extremie heat of the sun for hours at a time. That it not only 

 survives under such conditions but seems even to court sunshine 

 has doubtless given occasion to its specific name heliophila. The 

 water in which it thrives is often deeplv laden wuth sediment and 

 this at times may shield it partly from the sun's rays, but when 

 the water IS clear or the sponge is exposed to the air, it receives 



