and other Siliceous Bodies. SJ 



1000th to the 2000th of an inch in diameter, and the globules 

 vary from the 1000th to the 2380th of an inch. In other parts 

 of the interior of the fibre which are exposed by these sections, 

 there are globular bodies occasionally to be seen of a much 

 larger diameter, some of them measuring the 300th of an 

 inch : these are frequently quite opake ; but occasionally they 

 are somewhat semipellucid at their margins, and possess all 

 the characters which are usually observed in the young gem- 

 mules in a very early stage of their development, as they are 

 seen in other similar fossil specimens. Upon examining other 

 parts of the agate, there are large round opake bodies seen 

 imbedded in considerable numbers amid the fibres of the 

 sponge, which present all the characters both of structure and 

 situation that are observed in the numerous cases of the oc- 

 currence of the gemmules in the fossil state which I have be- 

 fore described. From the whole of these circumstances it 

 appears exceedingly probable that these minute vessels are 

 true ovarian ducts : the situation in which they are found, 

 the simplicity of their structure, and the nature of their con- 

 tents strongly favour this supposition. That they are not 

 vessels of circulation may be inferred by the existence of an- 

 other vascular system which I have described as occurring in 

 both the recent and the fossil species on the external surface 

 of the fibre, and within which vessels in the recent state nu- 

 merous very minute particles were observed, that have all the 

 characters which the true molecules of circulation in animals 

 so low in the organic scale might be expected to possess. In 

 another agate, that we have had occasion to refer to before, 

 and from which a few fibres are figured to prove the existence 

 of the gemmules in the fossil state, there are some appear- 

 ances of a curious nature that seem to illustrate the idea of 

 the vessels I have just described being ovarian ducts. In this 

 agate to which I allude, there are no appearances of well-de- 

 fined anastomosing fibres, but in place of these we have nu- 

 merous long and simple thread-like fibres (PI. I. figs. 5 and 

 6.), which appear to have suffered very much by decomposi- 

 tion, as their substance consists not of a regular tube or of a 

 solid fibre, but of a congeries of minute separate particles of 

 matter, as if resulting from the undisturbed decomposition of 

 a vessel in situ. Sometimes even the indication of the former 

 vessel is not present, but its original situation is pointed out 

 by the existence of lines of minute black bodies arranged in 

 straight or curved lines, such as they would assume if they 

 were inclosed within vessels which had taken such directions. 

 In other cases, these strings of incipient gemmules are seen as 

 represented in some parts of PI. I. figs. 5 and 6, contained 



