67 



water between two pieces of glass, until some of them are broken into 

 small pieces. In these fragments the spicula may be seen in situ, 

 arranged in the manner I have before described, and cemented toge- 

 ther by siliceous matter, which appears to abound in the outer inte- 

 gument of the gemmule. Upon measuring some of these minute spi- 

 cula in situ, I found their average length to be 1 / 7 - g of an inch, or 

 about equivalent to the diameter of a disk of human blood ; and their 

 average diameter ■ i S \ r c of an inch : so that they are of exceeding mi- 

 nuteness as compared with those found in the other parts of the same 

 animal. The rays of the stellate spicula (fig. 2) average 1 T of an 

 inch in length by r5 T 6 in diameter, and those of the skeleton have a 

 diameter of about -r^Vs of an inch. 



My friend Mr. C. G. White, of Poplar, to whom I gave a fragment 

 of this sponge, observed a circumstance attending the structure of the 

 ovoid bodies that had previously escaped my observation. Upon ex- 

 amining some of them which had been deprived of their fleshy inte- 

 guments, with a very high power, he found that they were frequently 

 furnished with a small pore or funnel-shaped orifice, situated about 

 midway between the two smaller extremities. The discovery of this 

 pore is an interesting circumstance, as it is a strong additional proof 

 of their gemmular nature. Link and Raspail, in treating of Spongilla 

 friabilis, describe a small yellow spot as existing on the outer tunic 

 of the gemmular bodies of the sponge ; and M. Gervais, in his obser- 

 vations on that species, describes the same organ and the manner in 

 which the sponge is propagated by the escape of granular bodies 

 through an orifice which exists at this spot. 



In the encrusted surface of this sponge I also observed numerous 

 round siliceous molecules, which were dispersed amid the spicula of 

 that part in abundance. The diameters of these, in many cases, were 

 equal to that of the surrounding spicula, but the greater number did 

 not exceed the half or a third of that size. 



The curious stellate spicula of the flesh are probably among the 

 earliest indications of the production of true bone in the higher class 

 of animals, in which we find it formed, in the plates of the skull and 

 other lamellated bones, from distinct centres of ossification; the origin 

 of each being a few stellate fibres or spicules, which are continually 

 produced from their centres outwards until they approach each other, 

 and, coalescing, form one uniform bony surface. In the crustaceous 

 and fleshy surfaces of some tunicated molluscs, we find an abundance 

 of minute stellate spicula of carbonate of lime ; and on the surfaces of 

 the bones of some cartilaginous fishes, we find a thin filmy stratum of 



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