36 



D. Externalappearance. 

 PI. I— IV. 



Spirastrella purpzirea (Lmk.) Rdl. is a very interesting sponge because of its extra- 

 ordinary variability. Dendy showed to what extent " Suberites inconstans" and " Spirastrella 

 vagabtnida" are variable-, and yet these are but members of a larger series. The species varies 

 in shape, color, size as well as in texture, in the general arrangement of the canal system 

 and the spiculation. Specimens like 1403 (PI. I, fig. 5), 300 (Pb I, fig. 1), 944 a (Pb I, fig. 2), 

 9 8 (PI. I, fig. 4 ), 612 d (PI. I, fig. 3), 948 c (Pb I, fig- 7), B.M. 11 (Pb II, fig. 2), B.M. 29 

 (Pb II, fig. 5), 1341a (PI- II, fig- 3), B.M. 2 (PI. III, fig. 4), B.M. 10 (Pb III, fig. 3), 42 6 b 

 (Pb III, fig. 1), 92c (Pb UI, fig. 5), M.M. 62 (Pb IV, fig. 1) do not resemble each other very 

 much — even less in reality than on the reproduction. 



As stated before I believe Spirastrella aurivillii Lindgr. and Vioa fiorida Ldfd. to be 

 identical with the sponge under consideration. Admitting this as granted, the sponge would 

 begin its post-larval life by boring into calcareous material like Cliona does. Lindgren (189S 

 p. 323) says about the "forma excavans" of S. aurivillii: "Weite Gange und Höhlungen in 

 Korallen bohrend". Lendenfeld (1897 s p. 108) writes about V. fiorida: "Der Schwamm bohrt 

 sich in alte Korallenskelette und andere, aus kohlensaurem Kalk bestehende, fossile und recente 

 Bildungen ein, und bildet im Innern derselben annahrend polyedrische, 1 — 15 mm. weite Kammern". 



However, I arrived at another conclusion. I do not think 6". purpurea ever bores in 

 the way Cliona does. I fully admit, that the sponge substance Lendenfeld and Lindgren found 

 in holes of corals etc. really belonged to the sponges they described; but they did not prove 

 that the holes were formed by the sponge. As far as I could see S. purpttrea grows in and 

 fills up the holes made by other organisms. It does not perforate the calcareous material but 

 uses preexisting holes. It may be that under certain circumstances the sponge can dissolve the 

 material gradually, but I never found a system of "canals" and "chambers" continuous with 

 the external parts as we easily find in Cliona. I examined series of microscopical sections 

 of decalcified specimens ; I always found S. purpurea covering partly the outside of say Litho- 

 thamnion, partly between the irregular deeper places, partly in holes etc. which were obviously 

 not made by the sponge. The calcareous Algae etc. are all covered or perforated, resp. more 

 or less destroyed or broken up by numerous organisms: ascidans, worms, polyps, Bryozoa, other 

 sponges, perforating Algae (and Fungi ?) and other plants, like we find them also in shells or 

 stones perforated by Cliona. Carefully removing thin incrustations of S. purpurea, one either 

 finds the substratum smooth and undamaged, or eroded and mixed with numerous calcareous 

 débris. In some specimens I found small yellowish spots, distinctly detached from the pure white 

 algae. Of course I took them first for the holes filled and made by our Spirastrella ; but by 

 closer examination and careful preparation none of them turned out to contain Spirastrella 

 the yellowish spots being the tops of some vegetable organism (Alga or Fungus ?) which could 

 be traced down for a couple of millimeters. Thus the substratum is broken up by numerous 

 organisms; in 1455 (Pb IV, fig. 6) I found a Thoosa destroying the Archaeolithothamnion, in 

 addition to Fungi a. o. but not the slightest indication that Spirastrella was perforating. Either 



