Studies on Sponges. II— IV. 491 



»Unsere Schwämme weisen darauf hin, dass die hornfreien Monactinel- 

 liden die Endglieder einer Reihe darstellen, die von den Hornschwäm- 

 men ausgeht.« Unfortunately this author does not give any proof for 

 this hypothesis and therefore it may be asked why ? Why do not ou the 

 contrary the Hornsponges descend from those Monactinellids ? Although 

 it is not yet proved that all the siliceous spicules in Sponges take their 

 origin in cells, as far as we know now, this is highly probable, and 

 what is stated for the spicules in certain groups of Siliceous Sponges 

 may be safely generalised over the other groups. Accepting that the 

 spicules always develop in cells, we may say that those cells represent 

 an older modification of ordinary connective-tissue-cells than those 

 which produce the spongin-fibres. In the oldest Sponges, the Hexacti- 

 nellids, we find no trace of spongin neither in recent not in fossil spe- 

 cimens. It is not made out whether Ceraosponges exist in fossil state, 

 but at any rate they are younger than Hexactinellids and do not appear 

 before Monactinellids. This is one of the reasons why it seems to me 

 more probable that the reverse from what von Lendenfeld says, is 

 true. Another argument lies in the canalsystem. All those Monactinel- 

 lid Sponges which are closely allied with the Ceraosponges possess a 

 canalsystem that is less developed than that of numerous Hornsponges. 

 I never found a system of canals and canaliculi as complicated as it is 

 in some Aplysinids; it belongs always to my third type. And even if 

 one shall find once a canalsystem of the fourth type or any other com- 

 plication in subdermal cavities or oscules or whatever , the great ma- 

 jority is very simply organised. 



VON Lendenfeld gives new arguments in favour of the Cerao- 

 sponges beiug closely related with Monactinellids. Till now however it 

 is not made out that the substance which sticks together the spicules of 

 many Chalineae^ Renicridae etc. is really to be compared with the 

 substance of the hornfibres. I think Sollas and Ridley were the first 

 who tried to investigate this point '. Ridley observed the substance in 

 question in polarizing light «in order to discover, if possible, some real 

 difference in optical properties between ordinary sarcode and keratosec 

 He found that »the horny matter, mounted in baisam, of Tuha^ Rhizo- 

 chalina oleracea. HircÌ7ìia lingua and Euspo?igìa cirgultosa polarizes 

 light, while that oiChalina finitima does not«. The substance of the latter 

 he called »pseudo-keratose«. This proves P that the horny matter 



1 Sollas in Ann. and Mag. (-5.) Vol. IV. p. 4S. — Ridley in Jouvn. Linnean 

 Soc. Vol. XV. (1881) p. 481. 



