and other Siliceous Bodies. 17 



the sponges of commerce, and which are probably incipient 

 gemmules. In a fifth specimen of agate that I procured from 

 Mr. Tennant they assume a very singular appearance, Some 

 of the gemmules are in a very perfect and beautiful state of 

 preservation, and in this condition are separated from each 

 other ; while others are observed, apparently, in various stages 

 of decomposition, presenting no definite outline or distinct or 

 regularly marked surface, but assuming the appearance of 

 having been resolved into gelatinous masses which have run 

 together into moniliform strings, in a manner very similar to 

 the mode of arrangement assumed by the discs of the blood 

 when vitality has ceased to exert its repellent influence upon 

 them, as seen in PI. II. fig. 3. 



Numerous other cases might be cited if it were necessary to 

 prove the spongeous nature of these interesting remains, and 

 the frequency of their occurrence in masses of agate; but I shall 

 content myself with selecting but one more ; and this I have 

 chosen, not only because it is one of the most perfect and il- 

 lustrative of the spongeous nature of these remains, but also 

 from its occurrence in a class of siliceous bodies which we have 

 not hitherto noticed. The specimen to which I allude occurs 

 in a siliceous mass from the island of Antigua, and is in the 

 possession of Dr. Robert Brown, who has favoured me with 

 the loan of it. The agate in which this beautiful sponge oc- 

 curs is nearly four inches square by about two inches thick, 

 and is part of an originally much larger mass. Its natural 

 surfaces do not afford any indication of its spongeous origin 

 when examined by a lens of an inch focus, and the cut or 

 fractured surfaces when examined in the same manner would 

 rather lead us to believe it to be a coral than a sponge, from 

 the whiteness of the tissue and the regularity of the arrange- 

 ment of the large excurrent canals. There are also plates of 

 spongeous tissue projected from the parietes of these canals to- 

 wards their centres, which cause them strongly to resemble 

 the sections of the polyp cells of corals ; but this resemblance 

 to the coral tribe ceases when a thin slice is examined as a 

 transparent object with a power of 150 linear. The whole is 

 then seen to be composed of the usual anastomosing fibres 

 which are so characteristic of the keratose tribe of sponges. 

 Even in the best preserved parts of the specimen the fibres 

 appear to have undergone decomposition sufficient to render 

 the characters of their surface somewhat indistinct, but not to 

 such an extent as to interfere with their mode of arrangement. 

 A section at right angles to the axis of one of the most di- 

 stinct and best preserved of the excurrent canals is represent- 

 ed by PL II. fig. 4. There are six large plates of reticulated 



Ann. £ Mag. N> Hist. Vol x. C 



