( 2r> ) 



wlierens the wall seems lo be IiomoucMjeoiis, llie conieiijs ai'e lioino- 

 geneous or rather ü,rainilar, apparently of a softer eoiisisteiiev than 

 the more rigid wall. This we eonelude from the fact that cnrved 

 or bent axial threads niulei- the microscope i-esemble curved or 

 bent indiarnbber tubes, tilled with a fluid or semi-tluid sid)slance. 

 Solid, flexible cylinders never show such abruptly bent figiu-es. 



A remarkable phenomenon is to be seen in broken spicules under 

 the influence of hydrofluoric acid. As stated above, the S})icopal is 

 dissolved in a peculiar way, the centi-al canal being hollowed out 

 in the shape of a funnel. If we now only take into consideration 

 the cases where the thread is bi'oken at the same place as the 

 spicopal, we see the thread gradually shrinking somewhat under the 

 influence of the hydrofluoric acid. However, the wall and its contents 

 do not shrink equally. The result is that the contents somewhat 

 pour out beyond the wall. It is not improbable that Bütschli has 

 seen this ; at least his illustration (fig. 24 on pi. XXI) strongly 

 resembles what we observed. But 1)Üts(:]iij explains it in another 

 way ; he believes the thread to be restricted "manschettenförmig". 



According to Bütschli the axial thread consists of a proteid 

 substance. With F. p]. Schulzk we can confirm this in the main 

 ])oints. Boiled in Millon's fluid the threads in ground spicules turn 

 yellow. This staining is especially distinct in pieces where a pai-t of 

 the thi-ead is lost, and where, consequently, the axis of the spicule 

 is }>artly uncolonred, partly fdled with a yellowish thread. Isolated 

 axial threads or threads })artly freed by solution of the spico|)al are 

 easily stained with iodine. Treated with nili-ic acid (25 "/J thev 

 swell somewhat and acipiire a faint yellow coloui-, Avhich becomes 

 darker by subsequent addition of ammonia. Pleated with nili-ic acid 

 the threads dissolve ; likewise in caustic potash. We may conclude, 

 therefore, that the central rod if not wholly, at least ])artly consists 

 of some proteid. Observed uiuler the j)olarisation microscojte no 

 trace of anisotropy could be seen. 



With regard to the styles of Tetlu/a /i/i/.ctii-/inn we thus arrixed 

 at the conclusion, that they are composed of an organic axial thread 

 and an organic spicnle-sheath, between which elements the spicopal 

 is deposited. We failed in demonstrating any trace of organic (s])iculiiie) 

 lamellae. But still we found, that under special ciivumstances 

 longitudinal, resp. concentric striae wei'e distinctly seen. We have 

 to look for an explanation of this fact. 



In order to avoid a possible misunderstan.ding or confusion we 

 wish at once to draw attention to the fact, hitherto rather neglected, 

 that one has to distinguish the various layers of spicopal from their 



