512 a monograph op the australian sponges, 



Skeleton. 



The fibres are highly colorable, more so than those of other 

 Spongidte. The connecting fibres consist of perfectly clear and 

 transparent Spongiolin and do not show a trace of being com[)Osed 

 of concentric layers. 



There is of course no doubt whatever, that they have been 

 formed like those of other horny sponges, but it is remarkable that 

 all the layers have precisely the same refractive power. 



Only the outermost layer, the youngest, appears slightly diflerent 

 under a high power in as much, as it absorbs coloring matter less 

 than the others and also refracts the light not so much as the 

 central parts. This is visible in a very striking manner in fine 

 sections. It must be assumed, that the outermost layer, which 

 consists of newly formed spongiolin is less dense than the older spon- 

 giolin in the centre and probably there is a certain amount of waterin 

 it, which is absent in the older central portions. I have some time 

 ago (1) expi'essed my opinion that the newly formed Spongiolin 

 is slimy. The structure of the fibres of our sponge are of such a 

 nature as to corroborate this. The Spongiolin is a hardened 

 slime, and it hardens by a process of drying, that is losing the 

 water with which it was originally mixed. 



This slime is poured over the fibres or foreign bodies by the 

 spongoblasts and thei'e it haixlens to spongiolin. 



The outer horny layers which enclose the foreign bodies in the 

 core of the main fibres, however, are clearly stratified. This 

 difference would point to a difierence in the formation of these 

 two. It appears that the connecting fibres are produced in a short 

 time and do not grow in thickness after they have once been 

 formed, whereas the main fibres occasionally receive a fresh coating 

 of spongiolin so as to strengthen them. 



No increase in strength in the connecting fibres is required as 

 the sponge grows in size, but the strain on the main fibres is of 



(1) i?. 11. Lendenfeld. Ueber Coelenteraten der Siidsee II., Mittheilung, 

 Neue AplysinidcB. Zeitschrift fiir wissenschaftliche Zoologie. Band 

 XXXVII., Seite 269. 



