3B 



for the most part of the still, abyssal depths of the ocean. 

 The colours of the flesh elements or so-called sarcode of 

 living sponges is subject to great variation even among 

 individuals of the same species. Thus in the ordinary- 

 sponge of commerce {Eiispongia officinalis) it runs through 

 various shades of brown, from yellowish grey to black, the 

 dominant hue in one variety being rusty red. In the birds'- 

 nest sponge {Pheronema Grayi), when brought up fresh from 

 a depth of 600 to 800 fathoms, the flesh was observed by 

 the writer to be bright orange, and this tint with shades 

 varying from the palest lemon yellow to brilliant scarlet is 

 characteristic of many sponges. The skeletonless Slime- 

 sponge [Halisarca Dujardinii) more usually resembles in 

 its natural habitat a little dab or dabs of red-currant jelly 

 scattered upon the surface of the rocks or seaweeds, though 

 at other times this carmine tint is replaced by the equally 

 brilliant hues of sky-blue or purple. Various shades of 

 green are common to many sponge forms ; a dark tint of 

 this colour being highly characteristic of the common 

 fresh-water sponge {Spongilla jiuviatilis), though in this 

 instance it has been recently determined that the colouring 

 agency is due to the presence of a minute parasitic vege- 

 table. The calcareous sponges {Calcispongice), including 

 Grantia and its allies, agree for the most part with one 

 another, and differ from the other sponge tribes, in that 

 their colour, when living, is almost pure white. This is 

 owing to the extreme tenuity and transparency of their 

 flesh and the refraction of the rays of light 6y the thickly 

 interlacing calcareous spicules of which their skeletons are 

 composed. 



Notwithstanding the very wide differences that subsist 

 in their external shape, in the colour, and in the composi- 

 tion and arrangement of the elements that form their 



