PORIFERA. I. loi 



means of the fibres to make out the place of the base. Between these fibres are only found irregularly 

 placed spicules and bundles of spicules, but coherent transversal fibres are not formed. Sometimes 

 the longitudinal fibres are especialh' found in certain parts of the sponge, while others show a more 

 irregular skeletal structure. The longitudinal fibres have an average thickness of 0-059 — 009""", and 

 are composed of rather many spicules alongside. From the skeletal tissue formed in this way, short 

 fibres run vertically towards the surface; these fibres spread in a penicillate way, and support the 

 dermal membrane. As before mentioned this membrane is provided with a reticulation of polyspicular 

 fibres; the ends of the supporting fibres, which are spread in a penicillate way, project through the 

 network of the dermal membrane, especially in the nodes of this network, and so the surface is finely 

 shaggy. The fibres supporting the dermal membrane, may in different places be of a somewhat dif- 

 ferent length, but most frequently it is between 0-5 and o-9""". The dermal membrane being thus 

 supported by fibres of the said length, a subdermal cavity is formed under it, into which cavity the 

 pores lead. Onh' a very .slight amount of spongin seems to be foimd in the skeleton uniting the 

 fibres here and there. 



Spicula: a. Mcgasclera are styli, evenly and most frequently slightly, only rarely somewhat 

 more strongly curved; sometimes the curve is in the middle, sometimes nearer to one end, and in this 

 case it is almost always nearer to the rounded end. The styli are fusiform, not only tapering to the 

 point, but also evenly towards the rounded end; the opposite end is evenly tapering, and only in the 

 very outermost part it may be somewhat more abruptly pointed. The thickness at the rounded end 

 is somewhat varying, and sometimes the needles are here ver}- thin, in a few cases they are quite 

 pointed, so that we get oxea. The length is between 0-38 and 0-47'""', most frequently it is 0-45"""; the 

 shortest ones are least frequently met with; in a few specimens the needles ma)- reach a length of 

 Q.-jmm_ xhe thickness in the middle is o-qi— 0-013'""' ; often the longest are not the thickest. Finer 

 and shorter needles, developmental phases, are also seen in small numbers; generally they are only 

 very little shorter than the fully developed ones. h. Microsclera : i. Diancistra of three different forms. 

 The large diancistra are of the well known form, called by Oscar Schmidt Pflugscharspangen , and 

 by Bowerbank trenchant bihamates . For the sake of description they may be described as sigmata 

 with long ends that are so strongly recurved as to form an only small angle with the shaft; the inside 

 of the recurved end thins into a thin, sharp edge stretching along the whole inside from the point to 

 the curve where it suddenly disappears; on the part of the shaft opposite to the recurved end a quite 

 similar edge of the same length is formed in the same wa\-; this edge ceases also quite suddenly at 

 the curve, and thus the curve forms a circular or oval hole. As the two edges of the shaft do not 

 reach the middle, the cylindric form of the shaft is seen here. The edges are so finely thinned that it 

 ma}- be difficult to see their inner limit. It is only very rarely the fact that both the recurved ends of 

 the diancistra are lying in the same plane, they are almost always more or less contort, often a quarter 

 of a turn, sometimes almost half a turn, so that the recurved ends are turned in opposite directions; 

 and not only the recurved ends are lying in different planes, but this is also the fact with regard to 

 the edges of the shaft, these edges being in the same, or about the same plane as the recurved end. 

 The length of the diancistra is between 0-137— 0-178""°, most frequently it seems to be o-ie-"'". The 

 thickness in the middle of the shaft is 0-008— o-oi'"'". Of these diancistra developmental forms are also 



