208 THE ANIMAL KINGDOM. 



on carefully removing Grantia ciliata, or Halichondria 

 panicece from its native rock, and placing it in a basin 

 of fresh sea-water, when they will presently pour forth 

 streams of the fluid from their oscula, and give full evidence 

 of life. 



Their propagation is by gemmation, or by winter-ova, 

 for a full description of which we must refer to Mr. 

 Bowerbank's papers in ' Trans. Micro. Soc., 1840/ arid 

 ' Johnson on British Sponges/ 



What we particularly want for an educational box is a 

 good section of sponge, showing the spicula in situ. The 

 following slides are, however, very useful, because after 

 examining the tri-radiate spicula of Grantia, the stellate 

 pin-shaped spicula of Tethea, the anchor-headed spicula of 

 Pachymatisma, and the peculiar bi-rotulate spicula of the 

 fresh-water sponge, Spongilla fluviatilis, we are able to 

 understand many of the miscellaneous contents of fossil 

 earth or recent sand, and discern not only the remains of 

 a sponge, but to what particular family an isolated spiculum 

 belongs. 



GEMMULES OF PACHYMATISMA. 



These are young sponges or gemmules ; they grow from 

 the sarcode body, and occur in great numbers towards the 

 base or root of the sponge ; at first they appear as little 

 knobs, arising from the cellular tissue, their stem lengthens, 

 they become detached, ciliated, and soon escape from the 

 parent sponge to whirl for some time in the water, and 

 finally fix upon their appointed habitat and grow into a 

 sponge. 



SP1CTJLES OF GRANTIA NIVEA. 



These are tri-radiate spicula of carbonate of lime. "With- 

 out sections of the sponge itself, or engravings, it is not 

 possible to explain or understand the beautiful arrangement 

 of these spicula for support and for defence ; many of them 

 project into the cavities of the sponge to prevent the en- 

 trance of foreign bodies, which would assuredly injure the 

 delicate fibres of its frame. 



