36 



PORIFERA. I. 



of the damaged specimens consists of four coalesced tubes, two of which are of equal length, while 

 the two others are shorter; the height of the specimen is 60""", but the lower part, probably a rather 

 long piece, is wanting. Whether we have here a ramification, or separate individuals growing near 

 each other and then coalesced, cannot be decided; it is perhaps more probable that it is a ramification 

 as the oscular canal of one of the small tubes runs into that of the large tube. The consistency is 

 soft, but not, however, very fragile. The colour (in spirit) is grayish yellow. The surface is finely 

 shaggy from the projecting ends of the fibres protruding to the length of a spicule. The dermal 

 membrane is thin and without spicules, it is supported by the underlying skeleton and pierced by the 

 ends of the fibres, and it is not separable. The pores are measured of a size of 0-029— o-oSg""™. O" ^'^^ 

 top of the sponge a circular oseitliim is found, which in one specimen has a slightly prominent margin; 

 it has a diameter of 5 — 7™". This osculum leads into an oscular canal continuing through the sponge 

 quite down into the stalk; the canal is through its whole length of about the same width as the 

 osculum, onl)- in the lower end it is somewhat narrowed. On the inside of the oscular canal the excurrent 



canals open rather close to each other, the size of the openings is about i — 2' 



/2 



'; no special arrangement 



of the openings is to be traced. The system of canals is highly developed, and the sponge very cavern- 

 ous. The chief canals have otherwise a very regular course, all beginning from the base or from a 

 spot uear the outside, and running parallel to each other arcuately upward and inward towards the 

 oscular canal; consequently all the openings in this canal are turned upward, and therefore in a longi- 

 tudinal section of the sponge a certain concentricity due to the course of the canals, is seen. All 

 over the outside of the sponge below the surface small, roundish subdermal cavities are found, which 

 b)- being seen through the skin, give the sponge a netlike appearance. 



The skeleton consists of a rather regular net oi fibres forming meshes, most of which are 

 quadratic, but some ma>' also be triangular or pentagonal; b\' far the greatest part of these fibres are 

 unispicular. Of the fibres those only, running from the middle of the sponge towards the periphery 

 arcuately upwards (the primarj- ones), are distinct and complete, while the fibres running at a right 

 angle to the former ones, and thus more or less parallel to the surface, are indistinct and incomplete. 

 A certain relation between the canals, at all events the chief canals, and the skeleton cannot here be 

 overlooked; for, the larger canals, as before mentioned, running upward and inward, while the skeletal 

 fibres are running upward and outward towards the periphery, these primary fibres will always be at 

 right angles to the canals, while the spicules of the secondary fibres are parti)' parallel to the canals. 

 Besides the fibres forming the net of meshes, some comparatively thick, polj'spicular fibres are found; 

 they begin in the lower part of the stalk, which is almost exclusively formed by such fibres, and 

 then they radiate up through the sponge branching off. The needles forming the net of meshes, 

 are at the ends united by a distinct mass of spongin. Scattered in the tissue some needles smaller 

 and finer than those forming the skeleton, are found, but only in small numbers. 



Spicula are oxea, rather thick and only very slighth- curved ; their length is rather constant, on 

 an average o-aoS'"™, but varying a little to both sides, and may go down to 0-178'"™, the thickness 

 varies between o-oi6 and o-oia'"", the shortest ones being commonlv the thickest; as before mentioned 

 a small number of shorter and finer needles are found, but they are by transitional forms evenly 

 connected with the others, and so they may certainly be regarded as developmental forms. 



