62 
Journal New York Entomological Society. 
[Vol. IV 
d, dorsal layer 0 f the phosphorescent plate penetrated by irregular tracheal branches., 
and rendered opake by numerous urate concretions imbedded in it; v, ventral phos¬ 
phorescent layer of the plate, with perpendicular tracheal stems whose branches, where 
they pass into capillaries bear lumps which stain brown with osmic acid, n, struct- 
urless substance ( coagulum ? ) filling the end of the last ventral segment. B. Iso¬ 
lated portion of the ventral layer of the phosphorescent plate, tr, tracheal stem sur¬ 
rounded by a cylindrical lobe; p, parenchymcell attached to the cylinder; capil. 
lary, without the spiral threads ; m , coagulum stained brown. C. a tracheal stem 
of the vential layer : at the fork of the brown-stained capillaries are lumps stained 
brown with osmic acid. D. a part of C. more highly magnified showing the remains 
of the tracheal end-cells ( tc ) enveloping the brown lumps ( m )—after Emery. 
In Luciola as well as in other fire-flies, including Pyrophorus , the 
phosphorescent organ or plate consists, as first stated by Kolliker, of two 
layers lying one over the other a dorsal one (d.) which is opake, chalky 
white,and non-photogenic, and a lower one (z/.), the active photogenic 
layer, which is transparent, d hrough the upper or opake layer and on its 
dorsal surface extend large tracheae and their horizontal branches, from 
which arise numerous very fine branches which pass down perpendicu¬ 
larly into the transparent or photogenic layer of the organ. Each 
tracheal stem, together with its short branches is enveloped by a cylin¬ 
drical mass of transparent tissue, so that only the short terminal 
branches or very fine tracheal capillaries project on the upper part of 
the cylinder. These finest tracheal capillaries are not in Luciola filled 
with air, but with a colorless fluid, as was also found by Wielowiejsky 
and others in Lampyris. 
These transparent cylinders, with the tracheae within, forming 
longitudinal axes, resemble lobules. These lobules are so distributed 
that they appear on a surface section of this plate as numerous round 
areas in which circular periphery the tracheal capillaries are arranged 
with the axially disposed tracheal end-cells. These “ tracheal end-cells ” 
are only membranous enlargements at the base of the tracheal capillar¬ 
ies ( Wielowiejsky). The cylindrical lobules are separated from each 
other by a substance consisting of abundant large granular cells (par- 
enchym cells ) among which project the tracheal capillaries. The cyl¬ 
indrical lobules extend to the hypodermis and come in contact only 
by their lateral faces with the parenchym. 
1 he structure of the upper opake chalky white layer of the phos¬ 
phorescent organ is, compared with that of the photogenic lower por¬ 
tion, very simple. In its loose, pappose, mass are no cellular elements, 
but when treated with different reagents it is seen to be filled with 
countless urate granules (guanine) swimming in the fluid it contains, 
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