142 



PORIFERA. II. 



recumbent; when bending over large subdermal cavities they are always recumbent. Sometimes the 

 dermal spicules are quite recumbent and scattered in the membrane, and then it rests on the main 

 skeleton, from which spicules may project through it. The pores are partly lying singly, scattered 

 among the projecting spicula-bundles, partly they are closely gathered over the subdermal cavities 

 where they form sieves. Their size was measured from o - oi8 — o - i2 mm . Oscitla may occur in very 

 varying numbers; most frequently they are rather few and scattered, but in a few cases they are 

 numerous, and may then in places be close-standing. Bowerbank says: <Oscula simple, dispersed, 

 numerous». They are round, with a sharp, sometimes a little raised edge. Their size was measured 

 from 0-5— 4 mm . 



The skeleton. The dermal skeleton, as mentioned above, is formed of close-set peuicillate, more 

 or less erect bundles of dermal spicules. They may sometimes be quite horizontal and scattered in 

 the membrane. The main skeleton consists of polyspicular fibres with up to six spicules alongside ; it 

 forms a rather irregular network of triangular and quadrangular meshes. Some longer fibres are found 

 running towards the surface, and they ma}' be connected by transverse bundles, so as to form more 

 regular, quadrangular meshes; these fibres may in places be rather numerous. A rather slight amount 

 of spongin is found in the nodes of the skeleton. 



Spicula: a. Megasclera. 1. The skeletal spicules are straight or slightly curved acauthostyli; 

 the curve is most frequently nearest to the rounded end. The point may be somewhat varying, from 

 rather short to middle long or rather long, in the latter case it is bounded by straight lines; in a few 

 cases the point is rounded. The spinulation is rather dense, but the spines are small; they are often 

 somewhat scattered in dots; most frequently the spines are a little closer gathered and also a little 

 larger at the head-end and near the point, while they are smaller in the middle. Bowerbank designs 

 this feature as incipiently spined . The spinulation ma} - be more or less marked, and when it is 

 slight, the spicule may be almost smooth in the middle. The point is most frequently without spines, 

 but sometimes they continue to the very end. The length varies from ca. 0-26 — o - 43 mm , and the thick- 

 ness from ca. o - oi— 0'024 mui . The small sizes are not frequently found. As well with regard to length 

 as to thickness a little difference may be found in different individuals. Developmental forms of 

 different sizes were found in small numbers; the young ones have a slight head-swelling and a rather 

 closely, but finely spined or knotty surface. 2. The dermal spicules are tornota; they are straight, 

 only sometimes a little sinuous. The points are short and bounded by curved lines, but end with a 

 little mucro. The tornotes are sometimes quite slightly constricted inside the points. The two ends 

 are almost never quite equal, but one is a little thinner and a little longer pointed than the other. 

 Their length is between 0-23 and o - 32 mm , and the thickness in the middle is 0-005 — o-oi2 ,nm . Develop- 

 mental forms, of which the young ones are styli, occurred, but in no great numbers. — In this species 

 it is almost always distinctly to be seen, which end of the tornotes is the original point, as it is always 

 thinner and longer pointed, while the other end is broader pointed and has most frequently a more 

 distinct constriction below the point (PI. XIV, fig. 5 e). These spicules also generally grow rather thick, 

 while one end still continues to appear as a distinct apex; this fact is, I suppose, what leads 

 Bowerbank to speak of «acuate tension spicula»; otherwise he is somewhat obscure, and in his diag- 

 nosis he calls the spicules of the dermal membrane <acerate , but further says: «Iuterstitial membranes. 



