66 



PORIFERA. I. 



mostly unispicular network is found. The lamellae orginate from the dermal layer and continue upward, 

 bending into the sponge (PI. XIII, fig. 2), and they appear to form continuous layers all round the sponge. 

 They consist of a dense feltwork of spicules lying in all directions parallel to the surface, but the spicules 

 are not quite so close-packed as in the layer of spicules closest to the dermal membrane. The lamellae are 

 pierced by the canals, and therefore they show a great many round holes. As mentioned, a network is 

 found between the lamellae. This network is rather irregular, its most regular feature is fibres running 

 vertically on the lamellae towards the surface; these fibres are most frequently polyspicular ; the other 

 network is unispicular und irregular. — This particular lamellar structure, which is found as well in the 

 thicker parts of the dermal layer of the sponge, as also especially marked off in the other skeleton, is 

 not easily explained, but I suppose it to be connected witli the way of growth of the sponge. 



The spicules of the skeleton are in the points of intersection united by a clear, but distinctly 

 observable mass of spongin; the spongin is developed, not only at the ends of the spicules, Imt wher- 

 ever the spicules are in contact with each other; therefore in the outer skin and in the lamellae, where 

 spicules intercross in all directions, the spongin is present in all the points of contact, and imparts a 

 great firmness to this skeleton. It is therefore frequently seen, when isolated spicules are examined 

 that they are provided with coats of spongin in several places, where they have been in contact with 

 other spicules (PL XIII, figs. 7, 8). 



Spiaila: 3,. Microsclera are evenly curved oxea, onl\- rarely they are a little more sharply bent 

 in the middle; sometimes the curve is a little irregular; they are of greatest thickness in the middle, 

 and taper somewhat towards the ends, the point itself, however, being only of a middle length; the 

 length varies between o'387— 0-476'"™ ; the thickness varies between o'oio— o-oiaS"'"". Shorter and finer 

 oxea are only found in small numbers, b. Megasclera. 1. Toxa; these are rather small, obtuse-angled, 

 and the ends are inclined backwards; they are of greatest thickness in the middle, and taper evenly 

 towards the ends. The full-grown and largest forms reach a length of oo6"'"\ and a thickness in the 

 middle of ca. o-ooaS™", but from this size downward all sizes and developmental forms are found down 

 to so small a size as hardly to be observed; thus they have been measured down to a length of 

 Q.QQ^mn. According to this these bows appear during the growth not only to increase in thickness, but 

 also to grow very much in length; the small forms, however, are always inscribable in the larger ones, 

 when the angle is the same; and a growth b}- mere apposition of parallel layers will increase the 

 length of the bows to a rather high degree; a growth in length by apposition, however, must certaiuK- 

 also take place, during which the inclined ends appear; these ends are not found in the smallest forms. 

 2. Sigmata. They are of a particular form, having in the middle a sharp, but obtuse-angled curve, 

 and the first part from here outward is straight, but then the ends continue arcuately and taper to 

 long points. Thus the middlemost part of this sigma reminds as to its form of a bow; the form ma\-, 

 however, be somewhat varying, and is sometimes rather irregular, which influences the length of the 

 sigma, measured after the greater axis. The length varies from 0-014— 0-05'""', the thickness in the 

 middle is ca. o-ooi'"'" in the larger, and a little less in the smaller ones. 



Remarks. In this .species granulous cells — cellules sphenileiises Topsent') — were found 



>) These cells, no doubt, correspond to Topsent's ^cellules spherulcuses <\ but in naming them so, I do not mean 

 to say anything as to their physiological signification. They are well known, and have often been mentioned, and different 



