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LITERATURE. 
1841 (a) BoweERBANK in Ann. & Mag. N. H. VII p. 72—74. 
1862 Scumipt, Die Spongien des adriatischen Meeres. 
1864 K6LLIKER, Icones histiologicae. I. 
1864 Scumipt, Supplement der Spongien des adriatischen Meeres. 
1892 Topsent.in Résultats Campagnes Prince Monaco. 
1897 LENDENFELD, Clavulina Adria. 
1898 TopsENT in Bull. Soc. Scient. Ouest. 
1900 TopsEnt in Arch. Zool. expérim. (3) VIII. 
1901 BürscuHur in Z. W. Z. LXIX. 
1902 
VosMAER in Kon. Akad. Wetensch. Amsterdam. Proc. meeting June 
1902. 
1905 VosmMAER & WijsMAN in id. Proc. meeting May 1905. 
EXPLANATION OF THE PLATE. 
(Fig. 1—21 are drawn 500 times magnified; fig. 22—24 still more magnified), 
1—3 Spirastrella bistellata; spinispirae carefully heated. In 3a only the 
central thread (carbonised) is drawn, lying in the central canal. 
. 4—18 Id. Influence of hydrofluoric acid. In figs. 4, 5 and 6 the acid has 
acted for a short time; only the spines begin to be dissolved. In fig. 7—12 
the process is advanced; the ““axis” becomes more and more obvious. In 
fig. 13—16 this is still more the case. 
„19 Tethya tincurium; oxyaster after carefully heating; distinct, (carbonised) 
central thread. 
. 20 1d. Middle piece of a stylus, carefully heated. Black (carbonised) central 
thread, entirely filling up the central canal. 
21. Id. Id. Shrunken, bent and broken central thread in the somewhat 
brownish central canal. 
ig. 22—24 Id. Id. Slightly more heated and brought into the hydrofluoric camera 
of Vosmaer & WIJSMAN; d. central thread, b. brownish layer around the 
central canal, s. brownish spiculum sheath. In fig. 22 it is seen at the begin- 
ning of the experiment; the sheath lies immediately on the external spicopal; 
the little granula are adhering particles, not belonging to the spiculum. In 
fig. 23 the hydrofluoric acid has penetrated the sheath and dissolved the 
peripheral layers of spicopal, the limits of which are marked c; the sheath 
remained in its place. In fig. 24 all spicopal is dissolved; only. the carbonised 
sheath s lies as a very delicate cylinder around the central thread. 
Leiden, 2 Jan, 1909, 
dr 
