186/.] DR. BOWERBANK ON ALCYONCELLUM SPECIOSUM. 351 



apical portion of the organ to the distal portions of the area ; while 

 in a smaller one from the same sponge there were only twenty-eight ; 

 so that it appears that no two of these organs are furnished with 

 precisely the same number of motive filaments, and that they increase 

 in number as the organ increases in age and size. The fibres on the 

 apices of the oscula of Mr. Lee's specimen, when immersed in water 

 only, were not above half the diameter of those which had been oper- 

 ated upon with caustic potass. 



The inner membrane of the corium in Mr. Lee's specimen is very 

 thin ; in a portion of it removed and immersed in water for exami- 

 nation there were numerous minute lentiform cells and a considerable 

 number of gemmular bodies, identical in size, form, and structure 

 with those with which we are so familiar in Halichondroid sponges, 

 and which also occur abundantly in the geuus Dactylocalyx ; but I 

 could not detect any traces of fibro-cellular organs. 



The more repeatedly and closely we examine the curious protu- 

 berant organs on the corium the more strongly we are confirmed 

 in the opinion that every part of Hyalonema mirabile is of a purely 

 spongeous nature. The discrepancy in the numbers of the supposed 

 tentacula beneath the apices of the oscular organs (no two appearing 

 to have anything like the same number of fibres in their circular 

 series), the invariable attachment of both their basal and apical ter- 

 minations to their respective membranes, their complete immersion 

 in the parietes of the oscular organs, the firm and solid structure 

 of the fibres themselves, and the undoubted keratose structure of 

 the mass on which they are imbedded, all concur in proving them 

 to be anything rather than polypiferous organs. On the contrary, 

 in numerous specimens of Zoanthus sulcatusi in my possession, 

 dispersed in patches on the surface of Desmacidon Jeffreysii from 

 Shetland, the structure of the polypidom is widely different from 

 that of the protuberant organs of Hyalonema. In Zoanthus it is 

 simply formed of grains of sand cemented by coagulable lymph, as 

 in the sand-tubes of Terebella, and, like them, rapidly decomposing 

 after the death of the animal. In the polypidoms of the Zoanthus 

 on Desmacidon Jeffreysii no radiating fibres like those in Hyalonema 

 are to be found, nor could I detect any distinct remains of the 

 polypes that once inhabited them. 



7. On Alcyoncellum speciosum. 

 By J. S. BowERBANK, LL.D., F.R.S., F.Z.S. &c. 



Alcyoncellum speciosum, Quoy et Gaimard. 



Euplectella aspergillumy Owen, Trans. Zool. Soc. iii. p. 203. 



E. cucumer, Owen, Trans. Linn. Soc. London, xxii. p. 11/, pi. 21. 



A considerable number of this beautiful sponge have recently been 

 imported, and its natural history has again been the subject of nuich 

 interest among zoologists. The first notice of its existence occurs 



