230 DR. J. MURIE ON STEERE'S SPONGE, 



With regard to the homology of the so-called root, body, beard, and dermal spicules of 

 at least the major section of the sexradiate sponges, I venture to offer a few mere 

 passing remarks. I apprehend that the presence of a veil or thin dermal layer of lattice- 

 work is far more constant among the Hexactinellida than is generally suspected, its deli- 

 cacy in many instances, I fear, causing its destruction in whole or part ere examination 

 of specimens is made. In Meyerina it is a very beautiful structure, readily apparent to 

 the eye even at a distance. It exists like a spider's web on the surface of the Euplectel- 

 lidEe. A fine sheet lies upon the Aslconema's felt. Labaria and Hyalonema both possess 

 such latticework. Holtenia and Bossella characteristically are veiled. Even Dendro- 

 spongia I am inclined to believe has such a covering spread all over its whorled branches 

 during life. In other genera the evidence borne by fragments leads to the conclusion of 

 its being a structural characteristic common to all. It seems to be for the support of the 

 dermal sarcode in which the pores are situated. 



The beard and whiskers, so termed by some authors, of such forms as Pheronema, 

 Mossella, Holtenia, &c, evidently are the homologues of the spicula, shorter, it is true, 

 composing the elegant sinuous frills of the Huplectella series. These latter frills, however 

 much differing in aspect, moreover correspond essentially with the whorled tufts of Den- 

 drospongia, and with the elevated obliquely ranged spicular vent-ridges in Meyerina. In 

 these and doubtless other forms they appear to be more or less modified spicules in direct 

 relation with the true skeletal vitreous fibre, and by or to which the finer dermal lattice- 

 work is attached. 



The long knitting-needle-like bundle of the glass rope in Hyalonema, the anchoring 

 spicules so well known in Holtenia &c, and the hairy-like bunch of lengthened spicula 

 at the root of Euplectella, have all strictly a homological relationship. Indeed nearly all 

 the Hexactinellida that have been procured in any thing like a perfect condition offer 

 some remnants, representing spicula specially adapted to retaining a hold of foreign 

 bodies to which they are rooted, or the so-termed roots are sunk in the sand or mud. 



Thus, again, however unlike may be the pattern of the vitreous fibre composing the 

 body or basis of such forms as Myliusia and Iphiteon, as contradistinguished from that 

 of Crateromorpha, Habrodictyon, Enplectella, Bendrospongia, and Hyalonema, whether 

 the sponge be shallow, cup-shaped, tubular, branched, or more solid, this, so to speak, 

 basal or body-fibre of simple, fused, or compactly built sexradiate spicula has a common 

 homological significance. 



However much modified, then, I am inclined to think the whole of the Hexactinellid 

 group, besides their bond of unity in six-armed spicula, are each provided with well-deve- 

 loped or traces of veil and root, superadded to such glassy fibre as more properly constitutes 

 their basal or body skeleton. 



Postscript. — It was not until some time after I had laid my paper before the Society' 

 that two contributions on the hexactinellid sponges by Dr. William Marshall, of Weimar, 

 in the Zeitsch. fur wissensch. Zool. *, came under my notice. The first published of these 



* " ITntersuchungen iiber Hexactinelliden," Z. f. w. Z. [1875, vol. xxv. (Supplementheft 2), pp. 142-243, pis. 

 xi.-xvii. ; and " Ideen iiber die Verwandtschaftsverhaltnisse der Hexactinelliden," Z. f. w. Z. 1876, vol. xxvii. pp. 

 113-136. 



