146 



ctften 



mass. Fungal hyphae are also 



of the specimens, more sparse, and forming an irregular reticulum 

 in the interior. 



The yellowish matrix, when examined in thin sections under 

 a high power, is usually seen to contain numerous very small 

 cells, which are more refractive and for the most part more 

 coloured than the substance in which they are embedded. The 

 latter may appear colourless in very thin sections, while the cells 

 in question are yellow, or brownish, or pale green. They are 

 usually elongated, and their sectional shape is elliptical or pyri- 



or 



may 



from 2 /x to 6 ju, or occasionally 8 /x, and their breadth 

 about half as great or more. Frequently no definite arrangement 

 can be distinguished, but occasionally in favourable places one 

 .can demonstrate that the cells are grouped in colonies, which 

 appear to be roughly spherical when small, elliptical or botryoida. 

 when large. The cells are arranged so that their length is radial 

 with regard to the colony, in which they form a peripheral layer, 

 one or sometimes two or more cells thick. Their lateral distance 

 from one another is variable, but generally greater than their own 

 diameter. When rather crowded, they are sometimes clearly 

 arranged in pairs or groups of four. The substance in which the 

 cells are embedded shows no structure, and might well be the 

 product of mucilage only. It is only here and there that colonies 

 of definite shape can be distinguished ; the scattered arrangement 

 of the cells in other parts of the matrix may be explained as 

 either due to flattening or distortion of colonies of similar form 

 and size, or to the colonies having had indefinite growth, so that 

 only young stages would show a regular form. 



From such details as can be determined, there seems to be no 

 doubt that the matrix has been derived from a gelatinous 

 organism belonging almost certainly to the blue-green Algae, 

 among which it would be classed under the Chroococcaceae. 

 Prof. G. S. West, F.L.S., who kindly examined the organism for 

 me, agrees that it certainly appears to be a blue-green Alga, and 

 compares it with Coelosphaerium, Naeg., but adds that it is not 

 exactly like anything with which he is acquainted* Its precise 

 determination must be reserved until living material, or such as 

 represents early stages in the formation of N'hangellite, can be 

 obtained. Conversion into bituminous substance must imply 

 extensive chemical changes in the mucilage, whereby the 

 original characters of the Alga may have been altered to some 

 extent as regards the spacing and form of the cells. Changes 

 have no doubt also taken place in the cell-contents, hence the 

 occasional greenish colour of the cells may be secondary and not 

 a remnant of their original pigment. On soaking or boiling a 

 section m water the cells undergo a curious change ; their cavities 

 become enlarged and often appear as though empty, bat, when 

 transferred to strong glycerine, they gradually regain their 

 original appearance. 



In some parts of the specimens the matrix shows no structure, 

 K! 6 , 1 ? <>t structure is often not abrupt but preceded by a 

 transitional boundary where the algal cells are collared or in- 



