1918.] THE SPONGES OF GUERNSEY. 11 i 



dominating. It is to this latter class that belong the thin brightly- 

 coloured masses that coat many of our rocks by the square 

 yard. The former are represented by the abundant simple 

 sponges that hang their white capsule-shaped bodies in myriads 

 from seaweeds and rocks. The spicules form beautiful objects 

 for the microscope, for they take all manner of forms, wheels 

 and spears and stars and rods and many variations of each. 

 They are easily obtained by dissolving the flesh in acid or caustic, 

 according to the substance of the spicule. 



In scientific language the sponges are known as the Porifera, 

 (Pore bearing), a very apt name, as a glance shows. Let us look 

 at a living specimen of the very common Salicisponge, Halichon- 

 dria. The rock we are looking at is coated with a layer of green 

 or red substance, rough to the touch and perforated with numbers 

 of holes of two very distinct sizes. The general surface is full of 

 tiny orifices or pores, while at intervals are larger holes situated 

 in the top of raised humps. A little fine sawdust dropped into the 

 water soon reveals the use of these holes. It soon disappears into 

 the general surface and in a short time reappears at the large 

 orifices, thus showing that a constant circulation is kept up in 

 the sponge flesh. The mechanism of this is revealed by the 

 microscope. Like all other living things, sponges are composed 

 of cells. 



A section of a sponge shows that the general substance is 

 traversed by countless canals corresponding in size to the 

 openings on the surface. At intervals the smaller canals 

 expand into chambers. The cells bordering these are provided 

 each with a single whip-like projection called aflagellum which 

 is in constant motion. The outward stroke has a smooth, 

 gliding motion, while the inward one is quick and sudden. 

 This constant process creates a current of water from the sea 

 through the animal's interior, thereby bringing oxygen and 

 food to the living cells. These small canals communicate with 

 the large ones through which the spent w^ater is driven back to 

 the sea via the large holes or osculse. In the simple Calce- 

 spongea like Grantia or Sycandra there is a single osculum 

 opening into the cavity within the sac-like mass, while in the 

 compound Silicospongia, Ceratospongia and Mynospongia there 

 are a great number. Hence the compound sponges are like a 

 large number of simple ones fused together. I will quote 

 Professor Huxley's apt illustration of the sponge menage : — 

 " The whole sponge represents a kind of subaqueous city, where 

 the people are arranged about the streets and roads in such a 

 manner that each can easily appropriate his food from the 

 water as it passes along.'* 



Each sponge contains both male and female elements, and 

 at certain seasons cells are modified into eggs and fertilised. 

 These are ejected through the osculae and develope into tiny* 



