SPONGES. 



CHAPTER V. 



SPONGES. 



bPONGiA FLUViATiLis ( SponxjHla fluviatiUs). — Plate XXI. 



On the 8th August 1839, I procured this at Lochend, where I had 

 seen something of the kind a number of years ago. The stones on the 

 east side of the Loch I found encrusted with it, overspreading an area of 

 from three to thirty inches. The substance is exceedingly fragile, in- 

 capable of resisting any force. The colour is of a dull dark green ; but 

 some are of a faint yellowish green. 



It generally rises in low pyramids or thickened ridges, with nume- 

 rous external orifices, seldom (at least at Lochend) exceeding one inch in 

 thickness. The surface of almost all the specimens is scantily studded 

 bv minute yellow globules. 



The ova are dispersed universally throughout the substance, many 

 as low as I could cut it with a knive from the stone ; but there they are 

 paler and seem immature. 



Two yellow ova, placed in a watch-glass, exhibited no motion ; 

 under the point of the knife, the shell cracked like an egg shell, and a 

 more tenacious matter escaped among the water. Subsequently, among 

 a number of ova floating in water, in different vessels, some seemed to 



M 



