462 Geolagical Society. 



bank lias little doubt that the vesicles are the fossilized gemmules of 

 the sponges which gave the form to the siliceous masses in which they 

 are imbedded. An agate supposed to have come from Oberstein, 

 presented characters which, Mr. Bowerbank is of opinion, indicated 

 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 in 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 horny 

 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 



* Microscopic Journal, vol. i. No. 1, p. 10. 



