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one specimen across for further examination. This I did with a 

 specimen to which I gave the number 338. At the base of the 

 sponge, which is somewhat broadened, I found between the "roots" 

 much sand, rather large pebbles and a number of shells. One of 

 these is a Voluta scapha Gmel. of about 10 cm. X 5 cm.; it 

 shows on its surface numerous holes of a boring sponge, which has 

 pierced the shell a good deal and which has already destroyed a 

 portion of the surface. Microscopical examination of the dried 

 sponge -substance in the interior of the Voluta proved that the 

 spiculation closely resembles that of the Poterion 338. The sponge 

 substance on the surface of the shell is continuous with that of 

 the Poterion. My supposition that Poter ion represents the free stage 

 of a boring sponge is hereby proved. I am not yet prepared to 

 say whether it is identical with one of the numerous known species. 

 I hope to be able to settle this later on and to give a full 

 account (with illustrations) of the subject. I shall then discuss why 

 only a small portion of Voluta is destroyed and the possible mode 

 of growth. As to the anatomy of the spirit-specimens now at my 

 disposal, a brief account may follow here. 



A longitudinal seel ion through the wall of the cup, somewhat 

 nearer its basis than its border, where the wall has a thickness of 

 about 25 mm., shows that the cortex has on both sides about the 

 same thickness, viz. 1 — 5 mm. The parenchyma shows large incurrent 

 and excurrent canals, both surrounded by a transparent tissue. The 

 main incurrent canals have a diameter of 0.5 mm., the main ex- 

 current canals of 0.5— 1 mm.; with the transparent tissue the former 

 are, on an average, 3 mm. the latter 5 mm. Both enter deeply into 

 the parenchyma; the former 15 — 20 mm., the latter 10 — 15 mm. 

 In their course through the parenchyma the incurrent canals show 

 several round apertures — the beginnings of secondary canals. 

 The mass between these main canals and the surrounding tissue 

 is composed of a crumb-of-bread like substance, and the trabecular 

 network of the skeleton. At this part of the cup the incurrent 

 apertures, stomions, are situated on the outside. They are congregated 

 into pore-areas of indistinct outline; these areas are nevertheless clearly 

 visible as dark brownish spots on a bufF-coloured background. The 

 areas have a diameter of a little more than a millimeter, and are 

 situated at about the same distance from each other. In some places 

 the areas are somewhat sunken ; in dry specimens this shrinkage goes 

 a good deal farther. I have not been able to detect the stomions on 

 the surface; but sections clearly show that they are placed more or 

 less in rows which start from a common centre. They are the apertures 



