Objects for the Microscope. 199 



This action may be observed by the seaside student on 

 carefully removing Grrantia 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. Bower- 

 bank's papers in 'Trans. Micro. Soc.,' 1840, and '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 Gfrantia, 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 fluviatilte, 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. 



SPICULES 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 arrange- 

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

 them project into the cavities of the sponge to prevent the 

 entrance of foreign bodies, which would assuredly injure 

 the delicate fibres of its frame. 



Grrantia compressa is an abundant animal in the caves at 

 Tenby, and the Gouliot Caves in Serk. Grrantia dliata is 



