BRITISH SPONGES 



123 



Among the common objects of the sea shore is the horny 

 skeleton of the sponge Chalina oculata, which is frequently 

 washed on the beach by the waves, especially after storms. This 

 sponge is not likely to be seen between the tide-marks except 

 at the lowest spring tide, when it may be found suspended in a 

 sheltered crevice or cave. The skeleton consists of a fine network 

 of horny fibres, in the centre of which lie the spicules, imbedded 

 in the horny material. The spicules are short and straight, taper- 

 ing at both ends. 



The Bread-crumb sponge (Halichondria, panicea) is even more 

 common, for it is to be found on every rocky coast, encrusting 



FIG. 73. Halichondria panicea 



weeds and rocks, often considerably above low-water mark. It is 

 of a yellowish or pale greenish colour, and forms an incrustation 

 varying in thickness from one-twentieth of an inch to half an inch 

 or more ; and, like most sponges, should be looked for in narrow 

 crevices, under heavy growths of weeds, or in other situations 

 where it is protected from the light. Sometimes its free surface is 

 unbroken, except, of course, by the minute pores, and, here and 

 there, the larger openings that serve for the outgoing currents; 

 but when it is found encrusting a rock in patches of considerable 

 size, the larger holes all occupy the summit of a little cone 

 resembling a miniature volcano with its crater. This sponge is 

 easily removed from the rock with the aid of a blunt broad-bladed 



