256 
NOTES AND MEMORANDA. 
It has been suggested that their siliceous elements were removed 
and replaced by carbonate of lime, but this appears to be most 
improbable. 
Professor Eoscoe and Professor Schorlemmer agree in stating 
that they would require overwhelming evidence before they would be 
prepared to accept such an explanation of the present condition of 
these objects or of the fact of the substitution of carbonate of lime for 
silica, that such an explanation renders necessary. 
Count Castracane has published an account of a process by which 
he reduced numerous specimens of coals to very minute quantities of 
coal ash, and has stated that he found in these ashes numerous marine 
and fresh-water Diatomacege. Professor Eoscoe kindly allowed one of 
his ablest assistants in his laboratory at Owens College to prepare 
analyses of a number of coals according to Count Castracane’s method. 
The residual ashes of these preparations have been mounted micro- 
scopically by Professor Williamson, and in no one of them can a trace 
of a diatom be fouud. Beyond stating the fact, he is wholly unable to 
account for the discrepancy between his results and those of the 
Italian observer ; so far as his present observations go, he finds him- 
self compelled to conclude that we have no proof of the existence of 
Eadiolarians or of DiatomacesB in the British carboniferous rocks. 
A short discussion ensued, in which Sir Joseph Hooker, Professor 
M‘Nab, and Dr. Bayley Balfour took part, the views expressed coin- 
ciding generally with those of Professor Williamson. 
Preservation of Planaria. — Dr. Arnold Lang, of Bern, whilst 
staying at the zoological station at Naples this year was constantly 
occupied in the endeavour to find a method of preserving the Planaria 
which was not only fitted to preserve the exterior form and colour 
of such tender beings, but would also preserve their histological 
structure for subsequent sections. He found that pyroligneous acid 
preserved the form and colour, but destroyed the histological struc- 
ture ; but in an old paper by Blanchard in the ‘ Annales des Sciences 
Naturelles ’ he met with the statement that the writer used “ liqueur 
salin hydrargyrique.” He therefore tried chloride of mercury, and 
succeeded beyond his expectation by using the following mixture : — 
100 parts by weight of distilled water. 
6-10 „ „ chloride of sodium. 
5-8 „ „ acid acet. glac. 
3-12 „ ,, chloride of mercury. 
(i „ „ alum). 
The process is as follows : — A perfect specimen is carefully placed 
in a shallow cup of sea-water, and laid on its back. This being done, 
the sea-water is removed by means of a pipette, so that the worm lies 
stretched out flat ; a sufficient quantity of the mixture is then poured 
on its abdominal side, when it at first draws itself together a little, 
but immediately afterwards extends itself, and dies almost directly, 
stiffened in its natural shape. Any wrinkles that may be formed 
can easily be straightened with a brush. Half an hour afterwards the 
mixture is to be removed by a pipette, and 70 per cent, alcohol 
