BY R. VON LENDENFELD, PH.D. 83 



As we jndge of the relationship of different animals mainly by 

 their morphology, we are of course generally unable to decide 

 which of two similar forms is the ancestor and which the descen- 

 dant or whether the two are to be considered as brothers. 



Vosmaer's hypothesis is very ingenious although I do not see 

 that there are any facts proving its correctness. It is directly 

 opposed to the hypothesis previously published by me (Das System 

 der Monactinellidse, Zoologischer Anzeiger. Band 1884, No. 164.) 



Forms like these Ceraospongiaj with siliceous flesh-spicules may 

 enlighten us on this question. Their production may have taken 

 place in one of the following ways. 



1. They are descended from ordinary horny Sponges and the 

 flesh-spicules have been produced sua sponte. 



2. They are descended from the Desmacidonidse, the silicious 

 fibres of which have been converted into arenaceous or horny 

 fibres. 



If the second of these alternatives be true, then we will have to 

 consider the flesh-spicules as the conservative part and they would 

 represent the flesh-spicules of the Desmacidonidae, which had 

 remained unchanged whilst the fibrous skeleton was being 

 transformed. 



If the first of these alternatives be true, then we would have to 

 consider these Phoriospongise and related sponges, either as tran- 

 sition forms leading from true hoi-ny Sponges to the Desmacidonidse 

 or as the terminations of series, beginning with the ordinary korny 

 Sponges and ending with these forms. 



I quite agree with Yosmaer and others that further investigtions 

 will be required to settle these questions. To my own and 

 Vosmaer's publications on the subject the merit is due of having 

 raised the question. As however, these flesh-spicules are much 

 softer and more variable than the spicules in the fibres it seems 

 diflicult to understand that the latter should have vanished whilst 

 the former remained during the disilicifying process as Vosmaer 

 asserts. 



I would also not be inclined to suppose that the Desmacidonidse 

 are particularly closely related to these Sponges in the opposite 



