and other Siliceous Bodies, 85 



same species remains to be demonstrated from the fossil spe- 

 cies found in the green jaspers of India. 



On examining a thin polished slice of one of the series of 

 seventy before mentioned, I found a portion of the structure 

 in an exceedingly fine state of preservation. The greater part 

 of the tissue is composed of minute pellucid sponge-tubes, but 

 among these there are occasionally others of much larger di- 

 mensions. The central tubular cavities in these are large and 

 exceedingly distinct, and their external surface is furnished 

 with a sheath or coat of a darker green than the other parts 

 of the fibre, in the manner represented in PL III. fig. 1, seen 

 with a power of sixty linear as a transparent object. This 

 green coat to the fibre is evidently analogous to the vascular 

 sheath, described in my paper ee On the keratose sponges of 

 commerce," as portions of a reticulated structure ; is occasion- 

 ally to be indistinctly observed even with this low power ; and 

 when the same parts are examined with a power of 120 linear, 

 the presence of the reticulated structure can be proved be- 

 yond a doubt to an observer conversant with the similar tissue 

 in the recent sponges ; but fortunately there is one piece of 

 the tissue which demonstrates its existence in the most satis- 

 factory manner. In this piece, which is represented by PL III. 

 fig. 2, as seen with a microscopic power of 120 linear, a 

 portion of the fibre has undergone a slight degree of decom- 

 position sufficient to remove the horny or fleshy part of the 

 sheath, but leaving the reticulated vascular structure in a 

 state of preservation almost as perfect as the similar tissues 

 that occur in the recent sponges ; for the vessels are as beau- 

 tifully distinct when viewed with a microscopic power of 500 

 linear, as represented in PL III. fig. 3, as they are in the Au- 

 stralian and Mediterranean sponges. 



There are two other specimens in which the reticulated vas- 

 cular coat of the sponge fibre is preserved, for which I am in- 

 debted to my friend Mr. Chas. G. White of Poplar, who found 

 them in two fragments broken out of a diluvial flint. In this 

 case, it is evident that the two small pieces of fibre upon which 

 it is seen are extraneous parts of another sponge which were 

 imbedded in the one that originally gave form to the mass in 

 which they were found. The vascular structure in the small- 

 est piece represented by PL III. fig. 4, as seen with a micro- 

 scopic power of 120 linear, is very like that coating the fibre of 

 one species of the sponges of commerce from the Mediter- 

 ranean ; it possesses the same bold and distinct character, and, 

 like it, throws off short branches, which terminate abruptly in 

 cceca; but in the second piece, represented by PL III. fig. 5, 

 the character varies somewhat, and resembles the more com- 

 plex mode of disposition of the analogous tissues in one of the 



