406 Mr. J. 8. Bowerbank on the Spongiadee, 
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 Pl. XIII. fig. 4. with a linear power of 1020. 
I have never found a similar tissue in such a situation m any 
other recent sponge; but it is a remarkable circumstance, that 
the first indication of the existence of such 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 m 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 gelatimous matter, and im 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 imner 
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- 
