488 Gr. C. J. Vosmaer 



to do tbis. Spong-es with niany protruding spicules are nearly always 

 covered with sand-particles and all kiuds of detritus, wliicli probably 

 serves as food. But tbis arrangement is of course not so important if the 

 animals every moment come into new water, and tbus bave niucb cbance 

 of finding sufficient food. A remarkable fact is tbat in tbose specimen» 

 where tbe gigantic rods do not protrude mucb. very tbin, sbort rods do 

 so. Tbese are so tbin tbat tbey are more or less flexible; besides tbey 

 are sbort and tbus tbe pression and friction of tbe water has less influ- 

 ence. In wbat measure tbese minute rods may be more favourable for 

 tbe keeping of food in tbe modified condition of tbe Sponge, I for the 

 moment cannot decide. 



To solve these questions time and experiments are wanted. One of 

 the great advantages of Zoological Stations is tbat just bere and only 

 bere such biological problems can be worked out. In many groups of 

 animals we may begin to do so ; with regard to Sponges however we 

 must proceed with great care. Tbere is still too mucb systematic con- 

 fusion, owing to tbe fact tbat even tbe simplest anatomical detail» are 

 unknown. First of all a natural system, based on anatomy and not on 

 tbe occurrence of certain spicules alone, is to be made. We first must 

 learn a little in wbat measure the principal anatomical details are simi- 

 lar enougb to enable us to bring certain Sponges into one species. 

 Then we ought to make experiments with it and see under whicb cir- 

 cumstances tbey vary and then perbaps we maygive some explauation. 

 Without careful examination of differentspecimens oi the Leucoma above 

 mentioned. I never would bave taken tbem as belouging to tbe same 

 species. Once baving seen tbis, one inquires wbat has produced tbe 

 chauges and may perbaps find a reason: as I bave just been doing. 



Now we can return to our first question, about tbe difiference 

 between tbe varieties cramhessa and typica. Leucoma aspera var. cram- 

 hessa probably is an offspring of tbe var. gigantea but fixed again on 

 not moveable objects. Tbey bave still more or less the shape qì gigantea 

 and thougb as a rule ratber smootb, tbey are never so mucb so as tbe 

 big ones. But their size is considerably reduced, because tbey are no 

 more in tbe favourable condition of being moved. Tbis is of course a 

 bypotbesis, but a hypothesis whicb explains sometbing and may be 

 proved or rejected by experiments. 



Tbus tbe diagnosis of Leucoiiia aspera must be as follows. 



Leucoma with three kinds of spicules : rods. triradiates and qua- 

 driradiates. Ordiuary rods much thicker and longer than tbe rays of tbe 

 tri- and quadriradiates. Tbe latter form a more or less distinct gastric 



