PORIFERA. I. 



to the situation of oscula and pores have only been discernible in a few places; especially the skin 

 of the outer surface has only been kept in a few spots. As far as I have been able to examine the 

 facts they are as follows: On the inside of the cup distinct, sharply defined circular oscula may be 

 seen with the naked eye in abundant numbers. They are of a somewhat different size, of a diameter 

 from ca. I — 2""". When a piece of the skin is examined under the microscope many smaller openings 

 are seen decreasing in size quite down to o-i2""". On the outer side no greater openings visible to 

 the naked eye, are seen, but under a lens or a microscope numerous openings are found, of sizes mea- 

 sured from 0-029— 0-3""". The small openings of a size of about o-oag™™ are the most numerous, and are 

 generally gathered into groups. While thus the openings of the inside upon the whole are greater 

 than those of the outside, they are, as is seen from the above, not sharply separated with regard to 

 size, the greatest openings on the outside being greater than the smaller ones on the inside. The 

 openings of the outside, I suppose, act as pores and those of the inside as oscula. Numerous canals 

 of an average diameter of 2 — 3""" go more or less horizontally through the wall of the sponge; they 

 have the greatest width towards the outside. They are distinctly seen, when the skin and the skeletal 

 tissue supporting it is removed. The oscula of the inside, at all events the larger ones, are direct 

 openings of these canals. 



The skeleton consists of powerful polyspicular fibres branching up through the sponge from 

 the base where they are so closely jjressed together as to form a compact mass. They are thickest 

 below, and may here be coalesced into bundles of a thickness of a few millimetres; upward they be- 

 come thinner. They branch in a dendritic way ujd throiigh the sponge frequently anastomosing and 

 coalescing with each other. As the fibres are numerous and placed close together the whole thing 

 forms a very strong skeleton crossed by the horizontal canals mentioned above, which run in the in- 

 tervals between the fibres; the sponge is otherwise so closely interwoven with these fibres that the 

 soft parts are only little consj^icnous. The finest fibres form a close, irregular network filling out the 

 intervals between the principal fibres. On either side of the sponge an irregular network is also found 

 on which the skin is resting; from the nodes of this network the bundles of spicules arise that make 

 the surface finely spinulous. The fibres are firm and solid; their spicules are united by a clear mass 

 , * J. yCifj' of spongin which is not, however, so copious that it ma\- be distinctly seen to coat the whole fibre, 

 even if it is perhaps completely or for the greater part lined with a thin layer. 



Spicula: a. Megasclcra are oxea, very evenh- tapering, and evenly and slightl)- curved, some- 

 times straight, more rarely they are somewhat sharper curved; the length is between 0-417 — 0-53""", 

 most frequently it is 0-44 — 0-47'""'. The thickness is ca. 0-018 — 0-024""", the thickest ones being gene- 

 rally not the longest. In a specimen (from East-Greenland) the most frequent length of the needles 

 is 0-417'"™, and may be even less, and they do not reach 0'47'"'". Shorter and finer needles are found, 

 but only in very small numbers, b. Microsclera : i. Toxa; these are rather large, regularly formed 

 bows forming an obtuse angle; only rarely it is somewhat sharper. The ends form short, recurved 

 points. They are thickest in the middle, and decrease, but only, slightly, in thickness outward. Their 

 length is between o-ii and o-i6™™, and the thickness in the middle is between 0-004— o-oo7'"™. Besides 

 these fully developed bows, some finer, to exceedingly fine ones, are found; these latter are on an 

 average not much shorter than the thicker ones, only the very finest go down to a length of 0-057'"'". 



