Zoological Society. 



505 



sessed of a very interesting sponge through the liberality of Dr. 

 Cutting, of Barbadoes, to whom we are also indebted for the ' recent ' 

 Pentacrinus, « recent ' Pholadomya, and numerous other valuable do- 

 nations ; and as this tribe has met with the able attention of micro- 

 scopists, whose researches appear to have excited considerable inter- 

 est; — 1 have thought a brief account of the specimen would be ac- 

 ceptable to naturalists." 



" The peculiarities of this very beautiful sponge consist in the fol- 

 lowing distinctive characters ; the most remarkable of which is, its 

 being formed entirely of silex, the reticulate structure of the mass be- 

 ing composed of transparent vitreous tubuli, without any admixture 

 of keratose or calcareous matter ; the silex forming the mass itself, 

 and not, as in other instances, arranged as spicula in the horny mem- 

 branes ; consequently, it is perfectly rigid and sonorous when struck. 



" When viewed by a simple lens it exhibits a frothy glass-like 

 appearance : under a magnifying power of seventy-five linear, the 

 net-like meshes are seen to be composed of beautiful glassy tubes, 

 anastomosing one with the other in every direction, the external 

 surface of the cylinders having a rugged aspect ; the newer or last 

 formed portions appear to emanate from centres, and at certain 

 distances from spherical masses, from which straight tubes again 

 arise, thus forming the reticulate structure. 



" Amidst the interstices of the sponge are found numerous small 

 bodies loose and unattached (also composed of silex*), characterized 

 by Ehrenberg under the generic appellation of Xanthidium, of which 

 several species in a fossil state are described as occurring in flints 

 and other siliceous minerals ; this minute body may be described as 

 a spherical mass of tubuli, arising from a centre, each tubular spine 

 being terminated by an expanded conical aperture, and a strong re- 

 semblance is at once observed between these bodies and the mode of 

 extension in the newer portions of the sponge itself ; this fact, to- 

 gether with that of the perfect siliceous character of these minute 

 bodies, induces me to come to the conclusion that they are not di- 

 stinct, free animals, parasites to the sponge, but the gemmules of the 

 sponge, in which they are found f ; and I think their increase, so as 



* In testing the mineral character of the sponge a small portion was ex- 

 amined under the microscope ; then placed in a test tube, and upon the ad- 

 dition of dilute hydrochloric acid no effervescence occurred : it was then 

 dried, and again placed in the field of the microscope, when no change ap- 

 peared to have taken place ; upon submitting it to the action of the blow- 

 pipe, the only alteration was its losing its glassy aspect by becoming opake, 

 but it was not altered in form. 



[f Mr. Stutchbury seems to be perfectly unaware of the fact that species 

 of Xanihidium have been observed in a living state ; the genus, we believe, 

 was founded by Ehrenberg previous to his knowledge of the existence of si- 

 milar forms fossil in the flint. Nor is this the first time that they have been 

 mistaken for eggs, — not of sponges, it is true, but of a polype. See Turpin's 

 paper on Cristatella mucedo, Ann. Sci. Nat. vol. vii. p. 141. Ehrenberg 

 pointed out the error committed by Turpin. 



The bodies here mentioned may be the gemmules of the sponge, but if so, 

 they are no Xanthidium, but merely bear resemblance to this genus of In- 

 fusoria. — W. F.] 



Ann. §• Mag. N. Hist. Vol. ix. 2 L 



