406 Mr. J. S. Bowerbank on the Spongiadse^ 



the anastomosing points of the fibre into which one of them will 

 pass, while the other pursues the direct course of the great 

 canal. They appear to be invested by a gelatinous coat or sheath, 

 as seen at c in fig. 3, which represents a portion of the great 

 central cavity of a fibre and its contents by transmitted light and 

 a power of 800 linear. The cavity within the vessel is small 

 compared with its external diameter, the parietes being so thick 

 that it does not exceed a third or a fourth of the whole diameter, 

 as represented by PI. XIII. fig. 4. with a linear power of 1020. 



I have never found a similar tissue in such a situation in any 

 other recent sponge ; but it is a remarkable circumstance, that 

 the first indication of the existence of sudi vessels in the interior 

 of sponge fibres was afforded me in the sponge tissues which 

 abound in the moss agates of the neighbourhood of Oberstein, 

 and which I have described and figured in a paper " On the 

 Spongeous Origin of Moss Agates and other Siliceous Bodies," 

 in the 'Annals and Magazine of Natural History' for September 

 and October 1842. 



The external surface of the fibre is frequently covered with a 

 complex reticulated vascular tissue, a small portion of which is 

 represented by PL XIII. fig. 5. with a power of 800 linear. It 

 is probable, if the fibre were in its natural condition, that this 

 tissue would be found to surround the whole of the fibrous 

 skeleton. 



A few minute portions of the remains of the fleshy interstitial 

 substance were found adhering to some of the fibres. Upon im- 

 mersing these in water, and submitting them to examination 

 with a power of 300 linear, they proved to consist of a series of 

 well-developed regular cells, represented by PL XIII. fig. 6. The 

 parietes of the greater portion of them were thickly coated with 

 deep amber-coloured, fleshy or gelatinous matter, and in some 

 of them there was a large round or oval mass of the same de- 

 scription of substance, which in many cases nearly filled the 

 whole of the interior of the cell. 



It is much to be regretted that the specimen from which these 

 details are drawn is but a fragment. It has evidently been part 

 of a series of tubular bodies, cemented together by approxima- 

 tion, or of a series of tubular branches; the outer diameter of 

 the tubes being about three-fourths of an inch, and the inner 

 diameter about half an inch, so that the parietes do not exceed 

 one-eighth of an inch in thickness. 



Stematumenia. 



Gen. Char. Skeleton composed of solid, compressed, kera- 

 tose fibre, in which siliceous spicula and grains of sand are occa- 



