Annals of the Transvaal Museum. 
only witli two European species, Lampyris splendidula, studied by 
Max Schultze in 1864, by Wielowiejski in 1882, and by Bongardt 
in 1903 ; and Luciola italica, studied by Emery in 1884. 
The species chosen for my work was Photinus mar ginellus , a 
small, light brown fire-fly very common in the vicinity of Cornell 
University during June and July. Of several hundred insects 
collected during three summers, only a small number were females. 
The female, although having fitly developed elytra and wings, 
apparently does not fly, as I have found all those collected either on 
the ground or on some low plant near the ground. 
The female has a single somewhat spherical light organ in the 
centre of the fifth abdominal segment, and the light is much inferior 
to that of the male. 
The larva of Pliotinus marginellus has never been recorded, and 
I was never able to find it. Neither did I ever succeed in getting 
eggs to develop, although I made several attempts. 
All my work was confined to light organs of the adult male. 
These are in the form of two plates, completely filling the ventral 
part of the fifth and sixth abdominal segments. They lie directly 
upon the very thin hypodermis. The underlying cuticle is transparent, 
allowing free emission of the light. The main tracheae of the 
photogenic segments send numerous branches into the light organs, 
perforating the whole dorsal surface. 
Where a section of the light organs of Photinus marginellus is 
studied with the microscope, it is found to be composed of two clearly 
defined layers. The ventral layer is composed of fairly regular, 
polygonal cells filled with a dense content of coarse granules. With 
transmitted light these granules are a dull brown. With reflected 
light, in both fresh material and prepared sections, they show a 
peculiar chalky whiteness which has given to the dorsal layer the 
name of “chalky layer 57 . 
In 1857 Kolliker analysed the granules from the dorsal layer 
of Lampyris and found them to be crystals of urate salts. This 
analysis has been verified by recent workers, among them Bongardt, 
in 1903. Granules, identical in appearance, are to be found in the 
fat body in the photogenic segments of Photinus. 
The ventral layer differs widely in structure from the dorsal. 
The tracheae continue to branch even more profusely in an arborescent 
manner characteristic of the photogenic tissue. There is a striking 
feature of the tracheal structures in the ventral layer which is wholly 
different from that in the dorsal layer. Each of the larger branches 
coming through the dorsal layer is approximately vertical in its 
course. Each of these tracheal trunks with its branches is surrounded 
by a cylindrical mass of tissue which is transparent in fresh material. 
These cylinders are distributed through the tissue with considerable 
regularity. Between these are cells very irregular in size and shape. 
These cells are called the “parenchyma cells 55 . 
Near the periphery of the cylinders the small tracheal branches 
divide, sending out generally two, rarely three or four, traclieoles. 
These tracheoles are fine tracheal branches characterized by having 
no spiral thickening of the intima. When fresh material, treated for 
half an hour with .5 per cent, osmic acid, then for a few minutes 
with weak caustic potash, is placed under the microscope ventral side 
up, the tracheae can readily be traced. The outlines of the cylinders 
