492 G. C. J. Vosmaer, Studies on Sponges. II— IV. 



not always polarizes light and 2^ that true keratose or spongin seems to 

 occur as well in Ceraospoìigìae as in Chalineae etc. I have studied many 

 Sponges in polarizing light and have had the same result. I foimd that 

 light was polarized by the spongin of the following Sponges : Euspongia 

 officinalis (strongly), Cacospotigia cavernosa 0. S.. Aplysina a'èrophoha 

 Ndo., Velinea gracilis Vosm., Ectyon strongly , Remerà cratera 0. S. 

 (feebly), Renieraßligrana 0. S. (feeblyi, Clathria coralloides 0. S., Cl. 

 ulmus Vosm., Cl. elegans Vosm, (all strongly), Axinella polypoides 

 (feebly), Pachychalina, Crihrochalma variahilis Vosm. On the other 

 band I coiüd not see any trace of it in Aphjsüla sulfurea F. E. S. and 

 Siphonochalina coriacea 0. S. The fact that I found the homy sub- 

 stance in a typical Renierid [R. cratera 0. S.) polarizing light struck 

 me rather. I therefore renewed my investigations on this Sponge, and 

 I found that the »Kitt-Substanz« not only in the point just mentioned 

 agreed with true spongin, but that also the same granulous matter oc- 

 cured, Ijang in »Kuppen« (Schulze one above the other, just as 

 Schulze and von Lendenfeld described it in some Hornsponges 

 (PI. 29 fig. 4). In preparations macerated by means of boiling corrosive 

 Sublimat, a method that I can strongly recommend for isolating Sponge- 

 cells, this is to be seen very distinctly. In the same preparation I saw 

 cells which resembled so much the Spongoblasts of Euspongia. that I 

 am very much inclined to believe that also in Reniera the spongin is 

 formed in the same way as in Euspongia. Unfortunately I tili now, 

 have not been able to make really good sections of R. cratera 0. S. and 

 I have not found those cells in situ as Schulze illustrates of Euspongia. 

 But I think there can be but little doubt that they occur. 



According to what I said above we may suppose that some meso- 

 derm-cells of siliceous Sponges gradually changed into real spongo- 

 blasts. 



Probably certain qualities of the seawater or in general the loca- 

 lity where the Sponge grows is favourable to a strong developmeut of 

 spougin-fibre, and so more and more the latter may prevali and the spi- 

 cules remain in the background, tili finally under circumstances very 

 favourable for one, very uufavourable for the other, true Hornsponges 

 have been formed. 



It is true that my Suggestion is a hypothesis also, but I have given 

 some arguments in favour of it, a fact which cannot be stated of von 

 Lendenfeld's. 



Naples. Aug. 4, 



