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gemmules in an immature state, or in different stages of development, 
fixed to the fibre of the sponge ; and in another specimen, believed to 
have been received from the same locality, gemmules in different 
conditions were sparingly scattered amid the tissue. 
If this idea of the development of the gemmules i situ be correct, 
it will account, the author thinks, for the frequent occurrence of small 
detached patches of minute sponge-fibre in well-developed and large- 
sized tissue. Several other specimens, considered by Mr. Bower- 
bank to contain gemmules in different stages of development or de- 
composition, are described in the paper, particularly an agate from 
Antigua in the possession of Mr. R. Brown; and one from Ober- 
stein, which contained vast numbers of small, pellucid, yellow glo- 
bules, bearing a strong resemblance to the minute granules which 
occur in the gelatinous or fleshy sheath surrounding the fibres of the 
sponge of commerce, and which are probably incipient germs. In 
accounting for the preservation of the gemmules in a fossil state, 
Mr. Bowerbank refers to the covering of the ova of birds, fishes and 
reptiles ; and he says, it is natural to expect that the gemmules of 
the sponge should be similarly protected, and therefore preserved 
after the decay of the sponge from which they derived their origin. 
3. Vascular structure.—In a species of recent Turkey sponge, and 
in some others from Australia*, Mr. Bowerbank detected in the homy 
sheath which invested the solid fibre, minute anastomosing vessels ; 
but he has not observed a similar vascular covering on the external sur- - 
face of the two specimens of Spongia fistularis which he has examined. 
The co-existence, however, of this sheath with a tubular fibre, he 
states, he has discovered in specimens of Indian green jasper. On 
examining with a power of 60 linear a thin polished slice, he 
found that some well-preserved tubes, of greater size than the rest, 
had, on their external surface, a coating of a darker colour than the 
other parts of the fibre, and were evidently analogous to the vascular 
sheath of the keratose sponges of commerce. On employing a power 
of 500 linear, the presence of a reticulated vascular structure was 
exhibited as distinctly as in the recent sponge, particularly where a 
portion of the originally horny or fleshy part of the sheath had un- 
dergone a slight degree of decomposition. ‘This structure. Mr. 
Bowerbank has also detected in two fragments of flint-pebbles. 
The characters exhibited by this external coating are not the 
only evidences of vascular structure which the author found during 
his examination of the organic remains inclosed in moss agates and 
Indian green jaspers, for he discovered in the centre of the tube 
which exhibited the sheath, a dark thread penetrating the cavity for 
a considerable distance, and when examined with a power of 500 
linear, it assumed the appearance of a spiral tubular thread, frequently 
obscured by irregular patches of a substance which the author con- 
ceives may have been glutinous animal matter. In another specimen 
of green jasper the spiral course of this curious tissue was much less 
obscure, and when examined with a power of 800 linear its tubular 
* Microscopic Journal, vol. i. No. 1, p. 10. 
