18 NATURAL HISTORY OF OUR SHORES 



support exists. An example on our coasts is the " jelly 

 sponge " (Halisarca dujardinii). 



Ceratospongia. Those in which the mass is supported by 

 a network of horny fibres. Example : the ordinary 

 sponges of commerce. 



Calcispongia. Usually small simple forms, in which the 

 support is formed by an arrangement of spicules of car- 

 bonate of lime. Example : the common little Sycandra 

 and Grantia of our shores, shown in Figs. 5 and 6. 



Silicispongia. Those in which the support consists of 

 an arrangement of spicules of silica or " flint." Example : 

 the great majority of our local sponges. A very familiar 

 one is Halichondria (Fig. 7). 



With these details in mind we can proceed with our 

 investigations. 



Sponges love shelter, and while a few stunted specimens 

 may be seen attached to rocks and sea-weeds in exposed 

 situations, for the greater variety and more luxuriant 

 growth we must repair to sheltered situations, little caverns 

 and grottos or deep rock crevices. A photograph of a 

 little cave closely lined with a heavy growth of sponges is 

 shown in Fig. 9. This little cave or grotto, one of a vast 

 number on this coast, is not done full justice to in the photo, 

 only the Halichondrias showing. The spaces between are' 

 covered with a deep crimson form, Hymeniacidon, but 

 owing to its colour the plate does not register it, except as 

 dark shades. 



Halichondria, or the " crumb of bread sponge," is subject 

 to much variation in its growth. In dark crevices- it is 

 almost white, in a sheltered situation with a fair amount of 

 light it is green, and in intermediate situations yellow: 

 Sometimes, where not subject to much wave action, the 

 osculse are raised to a considerable height. An example of 

 this growth can be seen in the centre of the plate just 

 alluded to. Under other conditions they are even with the 



