PORIFERA. III. 



shaped part, but it gradually increases evenly in thickness and reaches its greatest diameter at 

 the upper end. To judge from a couple of specimens which have the upper end tolerably undamaged, 

 the sponge is here suddenly and slightly obliquely cut, with a plane upper surface, which perhaps has 

 had an oscular tube; it is thus of a slender obconical shape, and is generally quite slightly curved, so 

 that it may very well be compared with a horn, as Carter says; further the sponge has some more 

 or less distinct, ring-like contractions. The size is about the same in all the specimens in my material, 

 the length 30 4O mm , the thickness above 6 io mm . Carter's specimen had a similar size. The con- 

 sistency is bladdery but, on account of the firmness of the outer layer, somewhat solid. The colour 

 (in spirit) is yellowish white. The surface is smooth. The dermal membrane is a thin, but firm and 

 solid membrane, provided with close-lying spicules arranged in one layer. Oscula and pores: Carter 

 supposed that oscula and pores were placed in the upper end of the sponge, but his specimens were 

 damaged here; my specimens also are more or less damaged in the upper end, yet a couple are so 

 much undamaged, that they give some information with regard to the place and structure of the 

 oscula and pores. The upper surface of the sponge is, as said, somewhat obliquely cut and is thus in 

 the main plane; on this lie an osculum and the pores. The osculum is a nearly circular opening with 

 a slightly projecting edge, it has a diameter of 1-5 mro ; it is in both the examined specimens placed 

 close to the margin of the upper surface and a wide canal leads from it down towards the base of the 

 sponge. In the other part of the upper surface lie the pores, they are circular or oval and so close- 

 lying that a sieve is formed; the incurrent openings to a number of canals are seen shining through 

 the pore-membrane; the pores are of a size of 0-023 O'i2 mm . 



The skeleton: The dermal skeleton. The outer membrane is provided with spicules lying close 

 to each other in one layer, but they are not closer than that the membrane may be seen everywhere 

 between them; the spicules are parallel with the surface and mainly arranged in the longitudinal 

 direction of the sponge; on the inside of the membrane some spicules are found which are arranged 

 at right angles to the others and thus lying transversely, they lie singly or a few together. The 

 membrane thus furnished is a little projecting above in the circumference of the sponge, and here 

 the spicules also project; the pore-membrane, which covers the upper surface of the sponge, is pro- 

 vided with a skeletal reticulation, forming the meshes in which the pores lie; this reticulation 

 is for a great part unispicular and irregular. In the part of the membrane surrounding the oscular 

 aperture, there are some short fibres, directed towards the aperture. The main skeleton is of a regular, 

 dendritical construction; from the base fibres go upwards through the sponge; in the centre they are 

 most powerful, and from here fibres steadily bend outwards which, running obliquely upwards, go to 

 the surface; these fibres have a somewhat regular course and are parallel with each other, and they 

 are connected by transverse fibres, which, however, are placed more irregularly; the fibres are strong 

 and consist of many spicules; they have an average thickness of o - i2 mm , those in the middle being still 

 thicker; the transverse fibres are thinner. The distance between the longitudinal fibres is about o - 5 mm . 

 Above, the fibres spread themselves out and support the membrane of the upper surface, and the spicules 

 are here a little projecting. As will be seen the skeletal reticulation thus formed is rather regular, 

 and the skeleton is intermediate between a dendritical and a reticulate skeleton. In the skeleton a 

 distinct amount of spongin is found, which in most places may be seen to coat the fibres with a 



