PORIFERA. II. 99 



up on one of the branches it was still io mm . In the outermost ramifications the axes grow thinner, 

 and are here i' nm thick or a little less. The fibres consist of closely united spicules, but they are not 

 here all of them parallel to the longitudinal direction, a great part being arranged in other ways. If 

 we regard a transverse section of a stem a rather marked stratification is seen; this stratification 

 arises from the fact that layers in which the spicules are more or less parallel to the longitudinal 

 direction, and which are, therefore, in the transverse section seen to be cut, alternate with layers in 

 which the spicules are scattered but parallel to the surface. In the layers in which the spicules are 

 placed in the longitudinal direction, they are to some degree arranged in bundles. The described con- 

 struction of the axial skeleton is also distinctly seen in a longitudinal section. In the thinner branches 

 no stratification is seen. The axes most frequently show a slight spiral twisting, which is, however, 

 often very indistinct, or has quite disappeared, the spicules of the outer layer being scattered. In this 

 species the axes are most frequently not cylindrical, but of an irregular contour, often with edges and 

 keels; and irregular coalescings of various kinds may take place. The skeleton of the branchlets con- 

 sists, as usually, of a fibre which is inserted in the axis and continues to the middle of the axis where 

 most frequently several fibres meet. In this species these fibres have rather many spicules alongside; 

 to be sure, they become a little thinner towards the point, but even there they consist of several 

 spicules. The spicules of the part of these fibres that is inserted in the axis, are as usually spread 

 in a fan-shaped way in the longitudinal direction; in the thinner branches the inserted part of the 

 fibres of the branchlets is of about the length of a spicule, but in the thicker branches and stems 

 also the branchlets continue to the middle, and then the part inserted in the axis gets a considerable 

 length. In this case only the innermost part of the fibres of the branchlets, about to the length of one 

 spicule, is spread in a fan-shaped way. It must also be supposed that the spicula-layers of the thicker 

 axes mentioned before are layers of growth, and that the inserted fibres of the branchlets, with the 

 exception of the innermost part, were at an earlier time outside the axis. In the layer of tissue out- 

 side the axes some scattered spicules are found, some of which are situated just under the skin, partly 

 between the branchlets, partly reaching a little into their basal parts. In the axes spongin is found 

 cementing the spicules; it is most abundant downwards, and therefore the yellowish colour of the 

 axes deepens downward, and at the base it becomes brownish. The axes have the common, somewhat 

 hyaline appearance. 



Spicula: a. Mcgasclcra; these, as already indicated in the name of the species, are diactinal; 

 the) 1 are typical oxea with equal ends, without any discernible tendency towards styli. They are straight 

 or slightly, often a little irregularly, curved, or they have in the middle a sharp, but slight bend. 

 From the middle they taper a little towards the ends, but the point itself is rather short, or at most 

 of middle length; an especially marked off outermost point is often found. They have not rarely a 

 swelling in the middle. These oxea, as mentioned, show no tendency to become styli; on the other 

 hand, forms are found with one rounded end, but only singly; forms with both ends more or less 

 rounded are, however, also seen, and I am, in both cases, most inclined to regard these forms as 

 secondary or irregular ones. Between the needles in the axes and those in the branchlets the only 

 difference is that the former are generally shorter and thicker than the latter; besides, needles with 

 the mentioned sharp bend occur far more frequently in the tissue and branchlets than in the axes. 





