\V;ilcrs we find :i Iiir^ir (jval wliitc s|»ol svliidi is jess calcified lliaii the rest of 

 llie J)as!il wall, luiii^ formed \)y a net-work ol iriesiies, and the wiiile colour is 

 dm- to (lie fact thai the liglit is reflected from the numerous small surfaces of 

 wliich this net-work is c-omposr-d. In Mi'inlimni/iorin/i arciicn, Siiiillinri Irisfjinosd, 

 var. I'lmclhmn and Siii. iir<if)iii<iiiu Ihr; hasal wall is covered hy small snow-while, 

 round spots of a similar structure. As to the manner in wliich the calcilication 

 lakes place, we can distinguish hetween coin|)Ound and simjile walls, as a wall 

 in some cases calcifies as a whole, wliile in other cases it calcifies in more or 

 liiHH separated piec^!H, whicli at any rate u|) U> a certain period are se|)arated 

 from one anollier hy sutures, and these sutures are in some cases very distinct 

 lor a \itw^ liini', wliiUf in oilier casis Ihc^y disappear very (piickiy. 'I'liis concerns very 

 ollcii llic liiiiilal sv:ill, and is due to (he circunistance that this is very often 

 provided willi covering layers or sculpture of various kinds. As examples of 

 sjiecies willi simple walls v,v. may meiilir)n Mcmhrtiiiif/oni iiieiiihrdiiiicen, Elcclra 

 jiilimii, species of I he genera Oiiijiliocelln, ni/i/iolliati, riialfiiiioixirellti, and Slet/ii- 

 iiiifinrclld and also il sr-ems — all memheis ol the families liiccllariidiic and 



Si rniioiflliii iiiliif. 'I lie p.nls inio wliich a eoiii|)oiiiid wall can he divided vary 

 very greatly in size, and llir- smallest of them give the imjuessioii, nol only from 

 their exci-edingly small size, hut also from Iheir shape, thai they are calci- 

 lied cells, as they have the same ci-eiiiilalerj contour whicli as a rule seems to 

 disliiifMiisli llie eelodi Till celK in llir Hn/ozoii. 'I'liis lonii of calcilicalion, which 

 we niiglii I'.'ill »eell mosaic is lor instance roiiiid on llie hasal wall in Mi'iiihrimi- 

 jKini SiiiKiili, l-'liislni (Iniliiiiliild (\'\. XIX, lig. 10 v), J'otalhi cunciniui, ni/iiJOfxidiiKi 

 fiu'iicriisis Musk, Siiiilliiia LdiiHhoroui, as well as on the laleial walls of i'luslvd 

 si'iriildhi. (iradiially s<'veral of tlmse very sniall cellular areas fuse logelher lo 

 larg(!r ones, and in older zoom- i a the nniik of division may (piile ilisap|ieai'. In conlrast 

 lo Hie very {\in- mosaic we lind in Hie jusl-mentioncd species, olhei- sjx-cies pre- 

 seiil a mosaic c(Misisliiig of iiiui-h largi-r hut sliU comparalively small areas, 

 which caniuil very well he regarded as cells. This form of calcilication, which 

 we nii;',lil cill plale mosaic , wi' lind \eiy linely <levelo|)ed on Hie hasal 

 wall of I'liislid ^nnrifiDiis (\'\. XIX, lig. H a) :iiid wc may here give a detailed 

 desci'i|)liiin of ils .ippeaiance in lliis sjX'cies, which lik(; mosi Fliislrd species has 

 a peiiecHy nncah-ilied IVonlal wall. The coni|)osilioii of Hie dillcrenl walls can 

 hc'.t he seen, as everywhere in Hie Hni<i:iiii, allei lliey lia\c been boiled for some 

 linie in .'ilkali, oi li:i\c hern lic.'iled wiHi f.\ii ile .hnclle, which cvi'ii in a cohl 

 condiHon has a lar liellei ellerl lliaii hoiling alkali. Having dissolved all organic 

 pails willi such Irealniiiil, we lind as a rule a rcnv of scpiare or li('xagonal plates 

 along Hie middle ol every hasal wall, while il seems as if a similar longitudinal 



