II2 PORIFERA. II. 



chondroid structure; some polyspicular fibres are found, running without any regularity, and otherwise 

 the tissue is filled with irregularly scattered spicules. At a little distance from the surface the skeleton 

 by degrees gets a different character, fibres occurring here that run more or less perpendicularly to 

 the surface; in their outer part these fibres divide, and the outermost fibres formed in that way pierce 

 the surface in bundles spread in a somewhat penicillate way, and support the skin like pillars. Below 

 the skin, therefore, is found a great number of small subdermal cavities, or more exactly, one large 

 such cavitv. The height of the pillars, which is the same as that of the subdermal cavity, is on an 

 average o - 4 mm . Between the fibres no transversal fibres or transversal spicules are found. The men- 

 tioned pillars are by no means always perpendicular on the surface; they may be placed more or less 

 obliquely on it, and thus be somewhat recumbent. When the surface of the sponge is seen under a 

 magnifying glass, this fact is distinctly seen, as also, that in one part of the sponge the pillars are all 

 directed to one side, in another part to another side, and in other places again they are directed per- 

 pendicularlv upward; by this means a certain configuration of the many small areas in the skin may 

 appear, only, however, to be seen by means of a magnifying glass. The outermost spicula-bundles of 

 the pillars, which pierce the dermal membrane, consist entirely or to some degree of spicules shorter 

 and thicker than the other spicules of the skeleton. These dermal spicules may occur somewhat 

 differently in different individuals. In some individuals the projecting spicula-bundles consist almost 

 exclusively of these shorter needles, in others, on the other hand, they are found in smaller numbers, 

 and many of the long spicules are found in the projecting bundles. According to this it would seem, 

 as if in this feature some difference was found between different individuals. If, however, thin sections 

 perpendicular on the surface are examined, the fact seems to be that when an abundance of the long 

 spicules is found in the projecting bundles, many of the shorter dermal spicules are also found, and 

 the bundles are larger, while they are smaller, when consisting almost exclusively of dermal spicules. 

 It may be possible, therefore, that the mentioned difference is owing to a contraction, by which the 

 dermal spicides are drawn back between the spicules inside. With this view agrees the fact that 

 those of the specimens in hand in which the dermal spicules are less prominent and mingled with the 

 longer ones, are low and very densely shaggy, while the higher individuals are less densely shaggy, 

 and in them the projecting bundles consist almost entirely of dermal spicules. Vosmaer says 1. c. : 

 The spicules are kept together by a very slightly developed keratode or pseudokeratode ; I have not 

 been able to find spongin in the skeleton, and I suppose that none is present. 



Spicula: a. Mcgasclera are subtylostyli ; they are divided into two forms, not, however, sharply 

 separated from each other; one form, as before mentioned, forms the whole skeleton and is also found, 

 in larger or smaller numbers, between the spicules piercing the dermal membrane; the other form, 

 more or less mingled with the preceding one, forms these projecting spicula-bundles. The skeletal 

 spicules proper are slender, straight, or slightly, somewhat irregularly curved; they taper evenly to a 

 long point that may be a little shorter pointed at the extremity. The opposite end is slightly swollen 

 to a head passing evenly, without any marking, into the shaft of the needle. They are quite slightly 

 fusiform, being a little thinner below the head-end than in the middle. The length varies from about 

 0-45— o-65 n,m , and the thickness is 0-006— cooa/"" 1 . The shorter and thicker spicules in the projecting 

 bundles are somewhat fusiform, being thickest in the middle, and the point is not so long. Their 



