Structure of some SiUcious Sponges. 34*7 



bounding fasciculi near the pores are observed to afford attach- 

 ment to a very deHcate apparatus calculated for the further de- 

 fence of these passages from foreign bodies, and for assisting in 

 the production of the currents. To avoid erroneous hypotheses 

 in searching into the nature of this perplexing substance, it will 

 be of some advantage to notice every minute piece of structure 

 which may illustrate its mode of existence, explain its functions 

 or help to distinguish the species, and it will be proper here, 

 as in other parts of anatomy, to adopt a technical language for 

 parts that are of constant occurrence, and important in the 

 economy of the animal. Although the spiculum of this sponge 

 agrees with that of the spongilla friabilis in being curved, and' 

 pointed at both ends, it differs from the latter in being thickest 

 in the middle, and a little less in size. This double pointed 

 fusiform curved spiculum is met with in several other sponges, 

 and always occurs unaccompanied with any other form but its own 

 modifications, so that it affords a determinate and easy means of 

 subdividing the great tribe of silicious sponges into lesser groups. 

 We observe this first form of spiculum likewise in the Spongia 

 urens or tomentosa, cristata, coalita, oculata, prolifera, dichoto- 

 ma, palmata, &c., but in the four last branched species it is 

 very minute and imbedded in a tough ligamentous matter, 

 which, in the dried state, assumes a faint resemblance to the homy 

 tubular fibres of the S. communis. It would appear from ex- 

 amination of some tropical species, that the transition from 

 the silicious to the horny axis takes place by the spicula be- 

 coming more and more minute, and their enveloping matter 

 more tough and fibrous. 



The second remarkable form of silicious spiculum met with 

 in marine sponges, is that which presents only one pointed ex- 

 tremity, while the opposite end is either simply rounded, or is 

 dilated into a distinct spherical head, like that of a common pin. 

 In the species already frequently mentioned in this memoir, un- 

 der the name of Spongia panicea, and which agrees with the 

 characters given of that species by Lamouroux, (Hist, des 

 Polyp, p. 9Q. ) in forming irregular spreading masses more than 

 an inch thick, and presenting in the dried state a white cellular 

 texture, Hke hard bread, with a flat and very porous surface, 

 we have the most famihar and distinct example of the one- 

 pointed spiculum, The spicula of the panicea are silicious, 



