26 DR. J. S. BOWERBANK ON HYALONEMA MIRABILE. [JaU. 10, 



The peculiarities of the structures of these oscular organs some- 

 what resemble those of the inhalant organs of Geodia Barreiti, 

 described and figured in the • Philosophical Transactions of the 

 Royal Society' fdr 1862, pi. 32. figs. .'3, 4 & 9«, pp. 788, 792, 794, 

 and also in ' JNIonograph of British Spongiadse,' pi. 19. figs. 301, 

 302, and pi. 28. f. 354 «. 



The spicula forming the spiral column of the sponge are the 

 longest organs of this description that I have ever seen. They are 

 composed of numerous concentric layers, and are very similar in their 

 structure to the large spicula in Tethea cranium or Euplectella 

 aspergillum, Owen. The asperation of the bases of the spicula is 

 usually produced by a partial desquamation of the concentric layers, 

 apparently for the purpose of giving the base of the column a stronger 

 adhesive power to the central mass of the sponge. In form they are 

 identical with those of the skeleton fasciculi of the basal mass of 

 sponge, but vastly enlarged in their size and proportions to adapt 

 theni to their own especial office in the economy of the animal. 

 The normal condition of these spicula is that of smooth cylinders ; 

 but when immersed in the basal mass of the sponge, and also in the 

 lower part of the corium, they undergo a remarkable alteration in 

 shape, assuming very frequently the lorm of the well-known struc- 

 ture of the hairs of the Bat. In this case the alteration in form is 

 effected by the projection of a series of thin superposed layers of 

 membrane following each other, and secreting silex rapidly and in- 

 creasingly as they advance, until, each having progressed about the 

 space of 4 or 5 diameters of the central spiculura, they terminate 

 abruptly with a strongly denticulated margin. The silex intervening 

 hetween the external coat of these coronated masses and the surface 

 of the axial spiculum is not composed of concentric layers as in the 

 latter, but it is as solid in appearance as a mass of glass, as repre- 

 sented (PI. V. figs. 16, 17). 



These curious forms may be seen deeply moulded in the substance 

 of the lower part of the inner corium in which such spicula have 

 been imbedded. This singular structure is apparently to endow tliat 

 portion of the spiculum with greater prehensile powers than could 

 be obtained by a more or less amount of desquamation of the proxi- 

 mal portions of the spiculum. 



The curious cloacal column of this sponge is not without a parallel 

 in the history of the Sponyiadce, as in the British genus Ciocahjpta. 

 In C. penicUlas we have a series of cloacal columns projected from 

 the basal mass of the sponge, each of which has a central axis of 

 spicula connected together in a longitudinal direction, which extends 

 from the base to the apex of eacli of the columns. A rather stout 

 dermal membrane envelopes each of them, but is not closely adhe- 

 rent to the central axis as in Hyalonema ; on the contrary, it is sup- 

 ported from contact with it by a series of short stout pedicels of spi- 

 cula, the bases of which are immersed in the central axis, and their 

 apices radiate in every direction, forming at their junction with the 

 dermal membrane a most effectual sujiport to it. The spaces between 

 the central column and the dermal membrane, when seen by the aid 



