52 



PORIFERA. II. 



mens in hand this layer is very thin and of a darker colour. The stalk is straight, or more or less 

 curved; in the upper part it is most frequently rather straight, and the part carrying the branches is 

 always straight; while the lower part may be curved or bent angularly in different ways. The longest 

 specimen, which is broken below, but has root-branches, has a length of ioo mm , and the part carrying 

 the branches is i$ mm long. The smallest specimen is 28 mm long, and the part with the branches only 

 4 mm long. The colour (in spirit) is white to yellow, the stalk, on account of the coating, is of a lighter 

 or darker brown. The consistency is firm, but the sponge is fragile. The surface is smooth, only on 

 the root-branches the spicules of the coating layer seem to project a little. On the part of the axis 

 carrying branches, between the bases of these, a thin dermal membrane is seen, in most specimens 

 highly damaged; it continues on the inner part of the branches, but can be traced no farther. It is 

 supported by the spicules in the outmost part of the axis, and it is abundantly provided with micro- 

 scleres of all three forms. The pores are found in the very thin dermal membrane; they are round 

 and have been measured, as an example, to a size of 0-047 — O'lio/ 1 " 11 . They were especially seen in 

 the parts of the membrane that are stretched between the inward or upward turned side of the base 

 of the branch and the axis, and therefore [they are turned somewhat upward. They are only to be 

 observed with difficulty, and they are most easily seen when the preparation is half-dry. Immediately 

 inside the dermal membrane is found a system of lacunae, separated by membranes with circular 

 openings. A few larger openings were seen in the dermal membrane, which might possibly be oscula; 

 otherwise the possibility is also found here that the branches form oscula; to be sure, their spicules 

 are continued to the very middle of the axis, but this fact does not prevent that they may be hollow 

 and open into the system of canals. 



The skeleton. The skeleton of the axis consists of a number of fibres running parallel to each 

 other in the longitudinal direction of the axis, and consisting of spicules with the point turned upward. 

 In the interstices between these fibres the lateral branches are inserted. In a transverse section the 

 fibres are seen to be arranged circularly round the middle (PI. XI, fig. 2). Round the fibres again, in 

 the periphery of the axis, some spicules are found supporting the dermal membrane; these spicules 

 form no conspicuous layer, being often rather much scattered; in a transverse section, however, they 

 are generally seen tolerably distinctly. As they are arranged between the bases of the branches they 

 are not always quite parallel to the longitudinal axis. Some canals running in the longitudinal direc- 

 tion, are seen in the transverse section, between the dermal layer and the fibres. I have not been 

 able to decide whether they continue through the axis as longitudinal canals, or they are only sub- 

 dermal cavities belonging to the cavities into which the pores open immediately. Down in the stalk 

 no separate fibres are found, but it consists entirely of close-packed spicules, and irregularly arranged 

 canals run through it. Also kf this species a twisting of the lower part of the axis was observed in 

 some individuals. The skeleton of the branches, as in the preceding species, consists of bundles or 

 fibres of spicules turning the points outward. They are inserted in the axis between its longitudinal 

 fibres, so that they meet in the middle. The inserted part of the fibres of the branches is compressed 

 in such a way, that in a transverse section it appears to have a thickness of only a few spicules, 

 while in a longitudinal section it has the full thickness, or the spicules are spread in a somewhat fan- 

 shaped manner. The skeleton of the axis consists of styli with a mixture of subtylostyli. As before 



