Stiidies OH Sponges. II— IV. 489 



layer. The peripheral skeleton eonsists of triradiates (occasionally also 

 a few quadriradiates) and gigantie rods, sometimes with tliiu acerates. 



Leiiconia aspera var. typica is characterised by its extremely rougli 

 surface and thick walls. Cloacal-cavity as a rule circular in seetion. 



Leucoma aspera var. gigantea is characterised by its gigantie size, 

 its smooth surface and rather tliin walls. Cloacal-cavity sometimes cir- 

 cular. very often however elongated elliptical in seetion. Thin slender 

 acerates often present. 



Leucoma aspera var. cramhessa is characterised by its flatness and 

 its shape, resembling a cocks-comb (or a cabbage, Haeckel] . Surface 

 smooth, here and there a little rough ; walls thin. Slender acerates often 

 present. 



Of course more varieties will be found. For the moment I do not 

 think it wise to make more than the three mentioned. As I often said, 

 in cases where specimens do not show distinctly the characters of the 

 varieties, it is better to call them mn^Xj Leuco7iia aspera (0. S.) Vosm. 



III. Oll Haeckers entogastric septa. 



Haeckel has found that in some Calcareous Sponges the cloacal- 

 cavity (»Magenhöhle« H.) instead of being a more or less equal tube, 

 shows irregulär membranes which divide the tube into entogastric septa 

 as he calls them. He found them in Ascons, Sycons and Leucons, and 

 first (Prodromus) considered them of great systematic value, erecting 

 several genera for those Sponges which possessed them. In his Mono- 

 graph however he had given it up and considered the absence or pre- 

 sence of the entogastric septa of little systematic value. as he made 

 oniy varieties on it. 



In Leucotiia aspera var. gigantea I found those septa often, but by 

 no means always very strongly developed. In normal specimens the 

 wall of the Sponge is more or less equal in thickness as sectious show 

 easily. In some specimens however we see that here and there the inner 

 (cloacal) side is thicker than in other places forming finally a kind of 

 septum at about right angles to the wall. Now these septa often fuse 

 together tili they finally give to the Sponge-wall the appearance of the 

 intestines of so many animals (figs. 6. 7 PI. 28). In the figs. la. 2a, 

 4 a, and 8 I have given illustrations of the greater or smaller develop- 

 ment of these irregularities, seen on transverse sections. Fig. 8 is a 



