Br. S. B. Boll— On Fossil Sponges. 349 



sponges, and 2nd, the Spongiaires vermicides, or true Petrospongidce.^ 

 With respect to the first of these groups, M. Etallon observes : — 

 " There are among the testaceous sponges which do not enter into 

 the family of Petrospongidce, some that have their skeleton made up 

 of little needle-shaped spicula, which are merely held together by 

 the parenchyma or sarcode of the animal, and of which, in certain 

 formations, we find the scattered remains ; but in other species these 

 needle-shaped spicula are always anastomosed so as to form little 

 stars united together by the extremities of their rays." It is to this 

 group that he gives the name of Bictyonoccelidce, and he describes 

 these stellate spicula as being formed by the enlargement of the two 

 extremities of a slender cylindrical spicula, which thereby become 

 cone-shaped at the end, and unite, by the circumference of their base, 

 with neighbouring cones, to form a six-rayed spicula with a central 

 noeud ; and, in the centre of this knot or noeud, M. Etallon believes 

 that there exists a cubic space which is subdivided by vertical and 

 horizontal laminee placed in the axis of the rays into eight chambers. 

 There results from this arrangement a frame work composed of 

 horizontal, vertical, and radiating rods, having a knot at their point 

 of intersection, and this eight-chambered noeud may be regarded as 

 standing in the place of the octohedral structure of Mr. Toulmin 

 Smith. 



While agreeing with M. Etallon that there are certain sponges 

 constructed on a general plan of intersecting horizontal, vertical, and 

 radiating rods, a plan, indeed, which still obtains at the present day, 

 the writer is far from admitting that this is the ordinary plan on 

 which the spicular sponges are organized, and he has entirely failed 

 to detect any trace of that subdivision of the cavity of the noeud 

 into the eight cubic chambers described by M. Etallon.^ Moreover, 

 the manner in which it is suggested that the skeleton is made up — 

 for as its development cannot be traced in the fossil it can be nothing 

 more than a suggestion — is altogether opposed to what we know 

 of the growth of spicula in general ; and the study of the recent 

 siliceous and calcareous sponges gives no countenance to the supposi- 

 tion that radiating spicula are formed by the union of the rays. On 

 the contrary, as observed by Dr. Bowerbank, " However closely the 

 spicula may be brought into contact with each other, or with siliceous 

 fibre, they do not appear to unite or anastomose, while fibre, whether 

 siliceous or horny, always anastomoses when it comes into contact 

 with parts of its own body, or of those of its own species." ^ The 

 growth of the sponge-tissue is outwards, not interstitial, and the 

 parts once formed and fully developed undergo no further change. 

 Judging from analogy, the development of the spiculum always 



1 The Clionidce are, however, only the accidental occupants of the cavities in 

 which tliey are found, having located themselves in the excavations formed by 

 Annelida and the terebrating mollusks. For the most part they are spicular sponges. 



2 In some stellate spicula, probably in all, at the point where the central canals of 

 the rays unite in the noeud, there is an hexagonal space, as noticed by this author, 

 but the appearance of vertical and horizontal lamiuaj are referable to an optical efl'ect 

 of light. 



3 I. c, p. 5. 



