i 7 8 



PORIFERA. II. 



it is often more irregular and somewhat diffuse. The skeletal net, when seen in larger sections, is of 

 a peculiar appearance on account of the many canals running through it. They are present in very 

 large numbers, and run chiefly, at all events the larger ones, more or less horizontally through the 

 sponge from the subdermal cavities of the pore side to the oscula. In a transverse section, therefore, 

 they are seen as straight or somewhat curved, sometimes branched canals passing from one side to 

 the other, while in a section parallel to the surface they are seen as close-set round holes. A white 

 and little conspicuous mass of spongiu is found in the nodes of the skeleton; in the more solid basal 

 parts the spongin is a little more copious and more extended in the network than farther up. In the 

 dermal network no spongiu is found. 



Spicida: a. Megasclera. i. The skeletal spicules are acanthostyli; they are straight or, 

 most frequently, curved in different degrees, often nearest to the head-end. The point may be somewhat 

 varying in different individuals, from rather short to middle long. The spinulation may vary much in 

 different individuals; in some it is very dense in the whole extent of the spiculum, and then all trans- 

 itions are found to almost quite smooth spicules. Also the size of the spines is varying, from rather 

 coarse to very fine; the coarse spines are especially found in the highly spined needles. Sometimes 

 the spines are more closely gathered round the head-end of the style, and they are also often closely 

 gathered near the point. In some needles the spinulation continues out on the very point, in others 

 the point is smooth. The mentioned variation takes place especially from one individual to another, 

 but some variation may also be found in one individual. When all the examined individuals are 

 included, the length of the styli varies from 0-26 — 0-45™"', these being thus the extreme limits found, 

 but it does not vary very much in the single individuals; as instances may be given, 0-26 — o - 3i mm , 

 0-29 — o - 37 mm , 0-35— o-42 mm , 0-38 — o-45 mni . The thickness varies between about o-oio — o-020 m,n ; it is other- 

 wise also somewhat varying in the individuals, those with the longest needles having not always the 

 thickest ones. A few finer, slightly spined developmental forms were seen. 2. The dermal spicules 

 are tylota with spined ends; they may be straight or more or less curved, most frequently they are 

 evenly and slightly curved; they may be of about equal thickness throughout, but they are oftenest 

 thickest in the middle and accordingly fusiform. Generally the two ends are not equal, one being a 

 little thicker and with a roundish swelling, the other a little thinner with a more longish swelling, 

 which is most frequently less marked; the difference, however, is often slight or quite imperceptible. 

 These spicules are much less varying than the skeletal ones; their common length is 0-238 — o-298 mm , 

 sometimes up to o - 3i ram ; in individuals in which the skeletal spicules are of the greatest length, the 

 dermal spicules may also be of the longest, for instance 0-28 — o^" 1 " 1 long. The thickness is ca. 0-005 

 — oon mm , most frequently about o-oo8 mm . Of the dermal spicules a few developmental forms were 

 seen showing that they are begun as monactinal needles, b. 2Iicrosclcra. These are anisochelae pal- 

 matse of the fofi/iou-type and bipocilla. 1. The chelae are of the form common in the genus; the 

 tooth is of the same or about the same breadth as the alas, and of the same length or a little shorter; 

 at the smaller end the tooth and the alae are of equal size, and here the axis in the common way sends 

 off from the curve a short spur. At the larger end a longish tuberculum is found; at the lower end 

 the tuberculum appears together with the spur as a pear-shaped body. The chelae vary much in 

 size, and at the same time the dimensions are a little altered, the larger end of the smaller chelae 



