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K<)ij,iKF,R savs (1. (\ p. 04 — 05), ^.ponking ahout " N^m'doa spoyiffiosa'*: 

 "Aiissenlcni liiuloii sich daiiii iiocli iiacli dci' Aiifl()Siiii<>; fier Spicula 

 dui'cli Essigsaurc, zalilroiclie Lückcii, wolcho dicsc Hilduii,i>on eiitlialteii, 

 die allen von eiiier scjiai-feii Linie begrenst sind, wie hei DunMerviUa. 

 Bei Xardoti jilanhe ieli micli davoii überzeugt /ai liaben, dass diese 

 scharfe Linie der optische Aiisdriiek einer !selbstandip;en Schelde der 

 Spicula ist . . ."' What K()LI,ikkr means by the woi-d "selbstiindig" 

 becomes clear when we read that in every canal sj)icules project, 

 in Avhich, after treatment with acetic acid, "an der Stelle des in die 

 Flimmercanale hineinragenden Strahles der genannton Sjiicula zarte 

 Sclieiden leer znrück (l)leiben)". These sheaths are, according to 

 KoLLiKER, perhaps a "Rest von Bildungzellen." However, he adds : 

 "freie Spicula zeigen, der Einwirking der Essigsiiure ausgesetzt, 

 keine solche Scheide...." What is meant here with "freie" spicula is 

 not evident. It can hardly mean anything else than isolated spicules. 

 If they be isolated mechanically, the sheath is as obvious as in 

 spicules in situ ; if they be isolated chemically, then of course the 

 absence of a sheath is no proof at all. 



It is easy enough to repeat Köllik?:rs experiments, especially in 

 using specimens with thin walls, as e.g. LeiK-osoIeuia. If a fragment 

 of a wide tube of L. rarlnhHi.s Avhich has been cut open, is spread 

 out in water under the microscope, and carefully treated with acetic 

 acid, the carbonate of lime is seen to be gradually dissolved, and 

 soon the sheaths, with sharjdy delined outlines, exactly as described 

 by KöLLiKKR, are visible. The sharp outlines are especially clear 

 on spots where the sj)icules are wholly enclosed by })arenchyma; in 

 projecting spicules the conical sheath of spiculine is seen to remain 

 as a homogeneous, extremely thin film; still more strikiiig, j)erhaps, 

 is the phenomenon if the sponge is stained on the object glass, e. g. 

 with carmalumn (GRÜBf,KR). The carmalumn, which is generally some- 

 what acid, causes the calcile to dissolve, and stains the sheath purple; 

 the sharply dotined outlines (optical sections) appear dark-purple, 

 while the i)rojecting spicules are faintly ])urplish. If such prepara- 

 tions are examined in glycerine or in Canada balsam, the spots 

 where the carbonate of lime lias been dissolved, or where it is still 

 present, are hardly to be discerned. When we use the polarising micros- 

 cope, however, the i)resence of calcite becomes immediately visible. 

 Consequently, there really exists a special layer of organic substance 

 which tightly covers the spicule, which can be isolated with the spiculum, 

 but which cannot l)e sei)arated from it otherwise than by dissolving 

 the carbonate of lime. Doubtless it is this organic layer which 

 KöLLiKER called "Scheide". In this sense also Minchin uses the word. 



