( 22 ) 



The question now arises how far siliceous spicules are likewise 

 enclosed by such organic coats, homologous to the sheaths of the 

 calcareous spicules. We are of opinion that this is actually the case; 

 the delicate organic fdni wiiich we found covering the spicules of 

 Tethya we consider as the honiologon of the spicule sheath of 

 calcareous spicules. Such products have been already observed. Noll 

 (1888 p. 16-17) says: "Noch ist fur die Spicula von Dcsmncidon 

 Bosei eines Ueberzugs von organischer Substanz Erwahnung zu tliun, 



Hauptsachlich nacli Behandlung der Praparate mit einer 



Höllensteiidösung w^eniger deutlich niit Acidum pyrophos- 



phoricum, manchmal audi mit Picrocarmin wurde derselbe sichtbar. 

 Stifte, die isoliert, ohne Ueberzug von verkittendem Spongin, iiber 

 die Halfte frei aus dem Schwammgewebe hervorstanden oder audi 

 solche, die ganz frei lagen, w^aren besonders nach der Silberfarbung 

 gleichmassig mit einem lichtbraunen Ueberzuge versehen, der trotz 

 seiner geringen Dicke doppelte Konturen erkennen liess und die 

 Stifte gleichmassig überdeckte .... Die Spicula von Desmacidon 

 Bosei besitzen also einen homogenen hautartigen Ueberzug von 

 organischer Substanz, der verschiedene Farbstolfe aufjiimmt. Wir 

 wollen ihn als Spicula-Oberhaut bezeichnen . . . ." Although Noll 

 sees in this coat something else than what Kölliker found in calca- 

 reous spicules, we suppose them to be ecpiivalent. Just as Kölliker 

 indicates that his "Scheide", is perhaps a "Rest von Bildungszellen", 

 so Noll writes that his "Oberhaut" may be "der Rest der die 

 Nadeln bildenden Zeilen". 



Sollas described in the same year (1888) such a sheath, wdiich 

 became perceptible after treatment with hydrofluoric acid. Description 

 and drawing (1. c. p. XLIX, PI. XLIII, fig. 18), regarding the 

 spicule of "Dori/plere.s Demlyi", leave nothing to be desired as to 

 clearness. "Although at first sight the acid appears to remove all 

 the substance of the spicule except the axial rod, careful observation 

 will show that this is not the case, for a delicate film of organic 

 matter also renuiins behind ; it has the form of a hollow sheath, 

 corresponding in form and }»osition with the outermost boundary of 

 the original spicule ; between it and the axial rod the whole of the 

 spicule is completely removed. The spicule thus consists of a central 

 organic axis, surrounded by concentric layers of opal, the outermost 

 of which is invested in a spicule sheath of organic matter or rather 

 of organic matter in intimate association (chemical union ?) with 

 silica". Our results regarding the presence of such a sheath in 

 spicules of other species we hope to give in a next publication ; for 

 the present we deal only with the spicules of Tethya. 



