KOLLIKER, ON LAMPYRIS. 169 
in a small glass vessel and covered with a shallow dish, con- 
taining a drop of a solution of the same salt. 
12. The luminosity of Lampyris is dependent upon the 
will of the animal, and exists by day as well as at night, 
though very frequently absent in the day time; a circum- 
stance evidently depending simply upon the fact that these 
insects are, for the most part, nocturnal in their habits, and 
usually lie concealed in the dark during the day. Movements 
alone have no influence upon the production of light; and 
even in the night time, individuals may be noticed performing 
the most active movements, and yet showing no luminosity 
whatever. Nor, also, has the concentration of light upon 
the animals any effect; whilst they exhibit luminosity even 
when they have been kept for days together in the dark. 
13. Many irritants exercise an influence upon the produc- 
tion of light, amongst which the following may be noticed : 
(1.) Mechanical irritation —The crushing of the luminous 
organs, or even a slight pressure upon them, from without, 
invariably causes brilliant illumination. When the organs 
are divided into small portions, or torn in pieces, the lumi- 
nosity soon ceases. The light is also frequently manifested 
when the head or thorax of the insect is cut off or slowly 
crushed. 
(2.) Electrical irritation—If the whole insect, or even 
only its abdomen, when the luminosity is not present, is 
excited longitudinally by a powerful induction-current, the 
most brilliant illumination is instantaneously produced, which 
usually quickly disappears again when the current is inter- 
rupted. The same effect is produced when the poles are ap- 
plied directly to the organs, and very frequently also when 
the head alone is excited. 
(3.) Temperatures—From the experiments of Kunde and 
myself, which agree pretty nearly with those of former 
observers, a temperature of +40° to + 60° R., always excites 
a bright luminosity; and the same effect is produced, though 
more rarely and with less certainty, by a temperature of 
from — 3° to — 5° R. Under variations, also, of temperature 
amounting to about 30° C., the luminosity is produced, as it is 
almost always when the animal is transferred from a freezing 
temperature to the warmth of the hand. 
(4.) Chemical irritants.—In these experiments, the sepa- 
rated abdomen only was always submitted to the reagent, with 
which the part was in all cases kept completely moistened. 
a. Caustic alkalies are powerful excitants of the luminous 
organs—caustie potass, in fact, acting im all degrees of con- 
centration, from 0°7 to 50 per cent. 
VOL. VI. ) 
