JOURNAL 
OF THE 
ROYAL MICROSCOPICAL SOCIETY. 
AUGUST 1891. 
TRANSACTIONS OF THE SOCIETY. 
VII. — On the Structure of certain Biatom-valves as shown by sections 
of charged specimens. 
By C. Haughton Gill, F.C.S., F.R.M.S. 
( Read 15 th April , 1891.) 
Plate VIII. 
In a paper which I had the honour to read before this Society on the 
19th of March, 1890, it was demonstrated that the “ striae, dots,” &c., 
of very various forms of diatoms were cavities of some kind, inasmuch 
as they could be filled with opaque foreign matter, e. g. platinum or 
the sulphides of mercury or silver. I added, “ Whether these lacunae 
are complete perforations through the silicious test or mere pits or 
depressions on the inner or outer surface of the valve, or more or less 
flask-formed cavities communicating by one or more canals with the 
inner or outer surface, or with both, cannot at present be resolved 
with any degree of certainty in the case of those diatoms which have 
the finer markings.” 
Since writing the above I have found among my slides a few 
fragments of charged diatoms so tilted as to give a clear edge view of 
the fractured shell. Some of these I have photographed, and they 
seem to me to show clearly that the lacunae in these cases at any 
rate extend from face to face and are not mere surface depressions. 
Photograph No. 1, taken from a specimen of Gocconema lanceo- 
laium, gives, at the points inclosed by the bracket, a picture of a 
broken edge which is not quite straight, and therefore not in sharp 
focus everywhere at once. It shows the mercurous sulphide filling 
the pores or lacunae and extending, apparently, from face to face of 
the shell. The same thing is seen in optical section only and confused 
by interference lines in the other margin of the valve as photographed. 
When examining the original slide (and others which I have not 
photographed) by help of a good 8 mm. apochromatic objective N.A. 
1*4, and careful adjustment of the light, I think that I can detect 
the presence of a limiting film of silica, on the outer face at least, cor- 
responding to the cell-cappings of the coscinodiscs. 
Photo No. 2 shows the same things in the case of the more finely 
dotted Stauroneis phoenicenteron . 
1891. 2 i 
