74 



Animal Life by the Sea-shore. 



altliough, curiousl}' enough, some belonging to various species are 

 articles of food for man in different parts of the world. Borlase, 

 in his " Natural Historj' of Cornwall " (published in 1758), stated 

 that Rhizostoma pulmo was frequently eaten in that county. 



With the exception of the minute, unicellular organisms 

 known as Protists, the Sponges occupy the lowest position 

 in the animal kingdom, and, indeed, not until the nineteenth 

 century was their animal nature definitely recognised. Their 

 great variety of shape, together 

 with the absence of organs of 

 sufficient size to be visible to the 

 naked eye, render them almost 

 incapable of any simple definition. 

 The scientific name of the group, 

 Porifera, refers to the fact that the 

 surface of a sponge is perforated bj' 

 myriads of little pores through 

 which water is taken in and caused 



FIG. 90. SYCON COHPRESSUM (pURSE-SPONGE) AND S. CILIATUM. 



to circulate through the body, being finally expelled through 

 larger exhalent orifices, which are often of considerable size. 

 This water current conveys the food, and also affords a means 

 of respiration for the animal. Only a few of our native Sponges 

 are sufficiently characteristic sea-shore organisms to find place 

 in a review which is not intended for the professional zoologist. 

 Perhaps the most striking is the little Purse-sponge, Sycon 

 compressum (Fig. go), so common at low tide in most rocky 

 localities. This Sponge is approximately ^'ase-shaped, but much 



