and Physiology of the Spongida. 37 



sarcode, and is most intense where most exposed to the light, 

 becoming less so in the lower parts ; this is the case in all 

 sponges, whether the colour be continued into the sarcode of 

 the body or confined to the surface. 



The colouring-matter may be diffused through the sarcode 

 like a dye, or in small pigmental granules ; the granules may 

 be diffused generally, or confined in pigment-cells, or both, 

 as if the former had been derived from the latter. Or the 

 colouring-matter may be confined to the spongozoa, which, 

 again, may only partake of it where most exposed to the light, 

 or possess it generally throughout the body. Lastly, the ova 

 on approaching the embryonal state may become coloured ; 

 and, in most instances, where the spongozoa and the ova are 

 coloured they present an intensified tint of the sponge to 

 which they belong ; so that in a red- or yellow-coloured sponge 

 the ova, when advanced in development, may be recognized 

 generally by being intensely red or yellow, as the case may be. 

 Yet in some cases they appear in the midst of a tawny -yellow- 

 coloured sponge as opaque white bodies when they attain their 

 embryonal state (see l Annals,' 1874, vol. xiv. p. 331). 



The same species of sponge may assume different colours ; 

 thus Grantia clathrus, Sdt. (= Clathrina, Gray), may in some 

 instances be vermilion-red, in others sulphur-yellow, and in 

 others grey -white, which is the most usual : here the colour 

 is general, and seated in the " granules." Esperia macilenta, 

 Bk., of our coasts, although generally tawny yellow, is some- 

 times vermilion-red. 



The colour, again, may be " fast " or permanent, or fade 

 after death, and on drying or preservation in spirit disappear 

 altogether, or leave a grey or brown tint only. Again, some 

 calcareous sponges (islathrina) which are opaque white while 

 living, become brick-brown when killed by being thrown into 

 fresh water ; while others ( Grantia nivea) retain their opaque 

 snow-white colour under all circumstances. The cause of this 

 has not been explained. 



Then, again, the tawny-yellow colour of the officinal sponge 

 of the shops, which, as before stated, is due to that of the horny 

 skeleton-fibre of which it is alone composed (which fibre is 

 analogous to the fibre of wool or that of the cocoon of a silk- 

 worm), is no indication of the colour of the skeleton-fibre 

 throughout the Spongida ; for it may be of all shades, from 

 colourless, grey, to brown, yellow, and deep dark amber ; while 

 in one instance at least (Spongia flabelliformis, Pallas ; Ian- 

 thella, Gray), where the soft parts are madder-brown and the 

 fibre deep amber, there are layers of carmine-coloured cells 



