78 I Harvey B. HoII — On Foml Sponges. 



little ueedle-.-^hapod spicula, Avhich are merely held together by the 

 parenchyma? or sarcode of the animal, and of which, in certain forma- 

 tions, 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 na ueof Dictt/onoeAdidcp, and lie vdescribes these stellate spicula 

 as being formed by the enlargement of the two extremities of a slender 

 cylindrical spicula, which thereby becomes cone-shaped at the end, and 

 unite, by the circumference of their base, with neighboring cones, to 

 form a six-rayed spicula with a central noeud ; and in the center of 

 this knot or noeud M. Etallon believes that there exists a cubic space, 

 which is subdivided by vertical and hoi-izontal lamina} placed in the 

 axis of the rays into eight chambers. There result^ from this arrange- 

 ment a framework composed of horizontal, vertical, and radiating rods, 

 having a knot at their jioint of intersection, and this eight-chambered 

 noeud mav be regarded as standing in the place of the octohedral 

 structure of ]Mr. Toulmin Smith. 



AVhile agreeing with M. Et.dlon, that there are certain sponges con- 

 structed on a general plan of intersecting horizontal, vertical, and rad- 

 iating 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. [In some stellate spicula, prob- 

 ably in all, at the point where the central canals of the rays unite in 

 the n(jcud, there is an hexagonal space, as noticed by this author, but 

 the appearance of vertical and horizontal laminae are referable to an 

 optical effect of light.] Moreover, the manner in which it is suggested 

 that the skeleton is made up — for as its development can not be traced 

 in the fossil, it can be nothing more than a suggestion — is altogether 

 opjioscd to what we know of the growth of spicula in general ; and 

 the study of the recent siliceous and calcareous sponges gives no coun- 

 tenance to the supposition that radiating spicula are formed by the 

 union of the rays. On the conti-ary, as observed by Dr. Bowerbank, 

 " however closely the spicula may be brought into contact with each 

 other, or with siliceous fiber, they do not appear to unite or anastomose, 

 while fiber, whether siliceous or horny, always anastomoses when it 

 comes into contact with parts of its own body, or of those of its own 

 species." Tiie growth of the sponge tissue is outward, not interstitial, 

 and the parts ()nce formed and fully developed undergo no further 

 change. Judging from analogy, the development of the spiculum 

 always proceeds from the centei-, and growth takes place by additions 



