64 



the length of the stratum, even to the edge of the periphery, where they become gradually 

 mixed with spicula of another sort (iig. 14) which are much thinner and longer (up to 8 Mm.) 

 very elastic, bristle-like, not enlarged in the middle, but evenly tapered in their whole length, 

 and terminating in an extremely fine elongated point. These bristle-like spicula form exclusively 

 the wide border which gives to the sponge so peculiar an appearance, and radiate on all sides 

 standing out horizontally from the circular rim. In the upper cortical stratum no trace is to 

 be found of these bristle-like spicula. On the contrary it derives its firmness chiefly from 

 spicula of another form, which are also found in the lower cortical stratum near the edge, and 

 now and then also in the interior parenchym. These spicula, which are particularly closely 

 packed round about the ends of the long fascicles of spicula that radiate from the inte- 

 rior of the sponge, and have here usually a transversal position, or stand at right angles 

 to the exterior surface and with their points turned outwards (see fig. 5) are very short (about 

 0.24 Mm. long) and pin-shaped (fig. 6 a) or furnished at one end with a globular enlargement 

 or head (see also fig. 8) while the shaft itself is rather strongly enlarged in the middle, and 

 at the other end sharply pointed (fusiformi-spinulate Bowerbank). In the exterior part of 

 this cortical stratum, we find again spicula of a somewhat different form, although most cor- 

 responding with those last named, from which they dift'er by the small development of the 

 head, this being often scarcely perceptible, and by the capillary form of the shaft scarcely 

 enlarged in the middle (fig. 6, c). These spicula, which are about of the same length as the 

 pin-shaped ones, are (see fig. .5) extremely closely packed, and stand all side by side at right 

 angles to the exterior surface which they penetrate with their extreme point. Tliese closely 

 packed e.xterior spicula form, as it were, a separate thin outer layer of the cortical stratum 

 (a— b) distinguished by a great degree of firmness, and by a lighter color than the other part. 



Tlie size of the different sorts of spicula is moreover, as alrea'dy remarked, rather 

 various; and more casual deviations in the form may not seldom be observed: this is espe- 

 cially the case with the pin-shaped spicula in the cortical stratum. The head is not always 

 round in these, but often shews at the extremity a more or less prominent peg-shaped pro- 

 cess (see fig. 10, a). In one case (fig. 10, b) this peg was quite unusually long and obliquely 

 inclined to one side, whereby the head came to he situated at the end of the first 4'!" part 

 of the length of the spiculum. In another case (fig. 9) there appeared in the middle of the 

 spiculum a few irregular enlargements or nodulous excrescences. Very seldom there were 

 found, especially in the lower cortical stratum, single spicula of the same sort which were 

 more than double as long (fig. 7). Otherwise the length of the pin-shaped spicula is tolerably 

 constant, and only varies within veiy narrow limits (from 0.91. to 0.28 Mm.). Between these 

 and the capillary spicula lying in the extreme dermal stratum there were also evident tran- 

 sition-forms (fig. 6 b) in which the shaft although still extremely thin, shewed itself evidently 

 enlarged in the middle. In some of these last the head was unusually wide, lancet-like or 

 top-shaped (fig. 6, d). 



This peculiar sponge occurs not rarely at Lofoten (at the fishing-places Skraaven and 



