PORII'ERA. II. 



J 93 



the sponge. Their common size was measured to between cro6 and o-i8 mm , and they may be still 

 larger. The pores, as mentioned, are confined to one surface of the sponge, but this is not the case 

 with oscula; these are found scattered on both sides, they form almost circular openings, and the 

 largest ones were measured to 2'5 m,n , these being found in the upper edge of the sponge. On the 

 pore side several openings are seen, from whose sizes it cannot be decided whether they are pores or 

 oscula; but, generally speaking, oscula and pores are separated by the size. 



The skeleton. The dermal skeleton consists in the common way of dermal spicules. On the 

 pore side thev form bundles or short fibres reaching from the edge of the subdermal cavities into the 

 membrane, and sometimes branching in between the pores. They are generally highly recumbent, 

 often quite horizontal, and spicules are also found scattered and lying horizontally in the membrane. 

 On the side that has no pores the dermal skeleton is less developed, and here horizontal spicules are 

 especially seen scattered in the membrane, which, to a great extent, is resting on the skeleton below. 

 The main skeleton is a quite irregular, mostly polyspicular reticulation, in which, however, also single 

 spicules are seen. Fibres are found running chiefly in the longitudinal direction of the sponge; they 

 may divide and unite again; they are polyspicular, but loose and little marked. Thus this species, 

 the form of which is more marked than that of the other species, also shows a tendency towards a 

 somewhat more differentiated skeletal structure. The fibres that are present represent primary fibres, 

 while the scattered spicula-buudles and single spicules may be regarded as representing the secondary 

 fibres. A distinct, but white and clear mass of spougin is found in the places where the spicules are 

 united; in places it may be seen entirely to coat the fibres with a quite thin layer. The sponge fre- 

 quently embodies sand and other bottom material. 



Spicula: a. Megasclcra. i. The skeletal spicules are styli; they are somewhat curved, 

 and the curve is most frequently- nearest the upper end; the point is short or rather short, sometimes 

 a little longer; it is often distinctly marked off and bounded by straight lines. Their length is 0-42 

 — o*57 mm and the thickness ca. 0010— o-oi3 mm . Developmental forms, down to quite fine ones, were 

 seen singly. 2. The dermal spicules are tylota with well developed ends; they are most frequently 

 straight and about cylindric; their length is 0-25 — o-34 m,n , the thickness varies from ca. 0-0028— o-oo45 mm . 

 While the fully developed tylota are of equal or about equal thickness in both ends, the singly 

 occurring developmental forms have one end a little thinner than the other and with a more marked 

 swelling, b. Microsclera ; these are birotulse of two sizes. 1. The large birotulse have at either 

 end a number of from twelve to twenty teeth; their length is 0-020 — o-028 mm , the thickness of the 

 shaft is 00014— o-oo2 mm , and the breadth across the circle of teeth is ca. 0-0057 — o-oo9' nm . According to 

 what is stated above, the number of teeth is rather varying, but some difference may be found in differ- 

 ent individuals; thus in one specimen the number is more frequently near or at the highest number, 

 while in the two others it only rarely reaches the highest figure. 2. The small birotulse have at 

 either end nine to fourteen teeth; their length is 00128— o-oi8 Tnm , the thickness of the shaft is ca. o-ooo7 mm , 

 and the breadth across the circle of teeth is ca. o-oo42 mm . As is seen, the two sizes of birotulse approach 

 each other very closely, and quite singly forms are seen of a size midway between the two forms. The 

 microscleres are found as well in the dermal membrane as throughout the sponge; the small birotulse 

 are everywhere numerous, the large ones scarce. 



The Ingolf-Expedition. VI. 2. 25 



