PORIFERA. II. 123 



places. Thus thev are often found on the edges of the compressed branches, but most frequently some 

 of them are then found scattered on the surfaces. In the highly flattened specimen mentioned before 

 the}' are found, partly on the edges, partly rather abundantly scattered over one surface, while on the 

 other surface only quite few are found; and they may, in the regularly digitate specimens, be found 

 almost exclusively on one surface. 



The skeleton is constructed quite as in a PacJiyclialina. It consists of polyspicular fibres passing 

 upward from the base and the middle, branching and bending to all sides in a sheaf-like way, and 

 going to the surface. These primary fibres are connected by transverse fibres that are placed perpen- 

 dicularly on them but form no coherent fibres. Thus a regular net of meshes is formed, which is 

 onlv less regular in the middle part of the bod)-. The meshes formed by the fibres are quadratic or 

 rectangular; towards the surface the transverse fibres are placed considerably more closely than farther 

 in. The distance between the primary fibres may be somewhat varying, and was measured to ca. ot8 

 — 0'4 m,n . The thickness of the primary fibres is generally about o-oo, mm . A distinct and most frequently 

 rather thick sheath of spongin is always found round the needles both in the primary fibres and in 

 the transverse ones. In the points of the fibres the mass of spongin is slight, and forms no sheath; 

 this fact is especially distinct in the points of the branches, where the growth more particularly takes 

 place. Quite as in the Chalinina, layers are also here found in the branches, which layers are more or 

 less parallel to the surface, and quite recall the structure of the outer skeletal layer, and these layers 

 have presumably during the growth of the sponge marked the close of a period of growth. The layer 

 arises by the fact that transverse fibres are here placed opposite to each other through the whole 

 extent of the layer, while these fibres on both sides of the layer, as well outside it as inside it, are 

 placed more scattered, often with rather long intervals. Then small short, primary fibres are found 

 reaching from the layer of transverse fibres a little outward between the primary ones, but continuing 

 no farther. Thus it looks, as if, by the beginning of a new period of growth, only some of the primary 

 fibres that project through the surface continue the growth. Both the mentioned structural features 

 cause the mentioned layers to appear as layers of more dense consistency, when a dried specimen of 

 the sponge is seen towards the light. Already Bowerbank mentions this feature, I.e. II, 312. Scat- 

 tered spicules are found rather copiously outside the fibres. 



Spicula: a. Mcgaselera are oxea; they are straight or slightly curved, and evenly, middle long 

 or rather long pointed. The spicules are very varying, both in length and thickness; the length varies 

 from about 0-15— o-229 mm , and the thickness from about 0-008— o-oi7 mm . The largest spicules are of 

 most frequent occurrence. It is, however, difficult to give the lower limit of the thickness, as some 

 developmental forms are found passing evenly into the fully developed needles. With regard to the 

 size of the needles, especially the thickness, some slight difference may be found between different 

 individuals. Styli are not rarely found between the needles; they are always shorter than oxea, and 

 they must surely be regarded as monstrous forms; in some individuals they are found more frequently 

 than in others, b. Microsclera; these are only of one form, isochelse palmatae of the peculiar 

 type before mentioned. When the chela is seen in profile, it looks as if the end of the tooth was 

 split into two branches, one of which continues towards the axis. The inner branch is the end of the 

 axis of the chela, which bends out from the tooth and in towards the axis. When the chela is seen 



