104 Rymer Jones, on Corethra plumicornis. 
pure water — and at once seal them up with a margin of gold- 
size. In this condition I found that they would live for 
several hours, and thus exhibit in perfection the action of 
the heart, and the ganglionic bodies appended to its walls. 
When this had ceased, I was enabled to study them for days 
together, and found, to my great gratification, that they only 
improve by keeping. Slowly their muscles assume a slight 
. degree of opacity, and shrinking, as by a sort of rigor mortis , 
leave spaces through which the minutest details of their ana- 
tomy are distinctly perceptible. The most delicate mem- 
branes, by a similar process, are rendered sufficiently opaque 
to be plainly visible, and the vesicles of the nascent limbs, in 
specimens approaching the .pupa condition, become clear and 
distinct. The nervous apparatus, constituting the ventral 
series of ganglia, forms a very beautiful object : in specimens 
thus preserved — the outer sheath, the structure of the ganglia, 
the composition of the internodal cords, together with the 
origin and course of the nerves, are all displayed in a most 
satisfactory manner, even the cross-markings of the muscular 
fibres are recognisable with the utmost distinctness. I have 
here one or two specimens of these larvae thus prepared, 
au naturel, which, although they have been upwards of a 
year in their present condition, will, I doubt not, when 
placed beneath the microscope, fully serve to recommend the 
process I have adopted. There is one precaution necessary 
in making these preparations, which, trivial as it may seem, 
will be found of much practical importance. In order to 
delineate specimens thus put up, while in the microscope, by 
means of the camera lucida, it is essential that the depth of 
the cells in which they are placed should be just such as to 
press sufficiently upon the enclosed larva to hold it steady 
while in a vertical position, otherwise it sinks in the sur- 
rounding fluid, and is continually subject to displacement. 
The manner in which I have succeeded in overcoming this 
difficulty is very simple. The cells that I employ are discs 
of thin sheet-lead, cut out with a circular punch, and per- 
forated in the centre by another punch of smaller diameter. 
These discs, when cemented to a glass slide with gold-size, 
are easily rubbed upon a wet hone to the exact thickness 
required, and the object so mounted retained in its place by 
the pressure of the glass, will be found to be as steady and 
manageable as if placed in Canada balsam. 
