BY R. VON LENDENFELD, PH.D. 327 



d. The fibrils of Hircinia. 



In the European Sponges belonging to the Genera Hircinia and 

 Oligoceras, and also in some Sponges not belonging to these 

 Genera, which I have found on our shores, we meet with a dense 

 mass of fibrillae, long threads with a nob at each end, which may 

 be considered as a peculiar kind of skeleton. They never form 

 the only skeleton of the Sponge, but are always associated with a 

 well developed hornfibre skeleton, and sometimes also with 

 siliceous spicules (Von Lendenfeld das System der Monactinellae.) 

 Their accessary appearance makes it not improbable that they are, 

 or belong to a parasitic organism. The researches which were 

 carried on to elucidate this point at the Zoological Laboratory in 

 Graz, under F. E. Schulze, by myself, and others, did not lead to 

 any positive result. The analysis shows that these fibrils also 

 contain a great proportion of nitrogen. 



2. The ground substance. 



The ground substance appears as a secretory product of the 

 numerous star- shaped cells imbedded therein and has a similar 

 chemical constitution as glue. 



3. Foreign bodies. 



Sponges are often rich in foreign bodies, which may be of any 

 nature, provided they have the proper size. Nevertheless certain 

 Sponges generally select certain foreign bodies. The most common 

 are sand and spicules of other Sponges, which, after the death 

 and decay of these, have dropped to the bottom of the sea. 



Ceraospongise nearly always contain, more or less sand and 

 other particles in their main radial, sometimes also in their 

 tangental fibres. Sometimes also such bodies are met with in the 

 ground substance of body or skin. They fall on the surface of the 

 Sponge, the Ectodermal epithel cells give way to them, they enter 

 the body of the Sponge and are lead to their place of destination. 

 Particularly interesting are pointed bits of quartz (sand) which 

 are selected with great care. They are always of the same shape, 

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