DEVELOPMENT OE THE OVAEIES IN THE BLOWFLY. 435 
appearances, in optical section, wliicli could be interpreted without 
difficulty, as Stein and Leuckart have interpreted them ; possibly 
the fine tubes are the fine tracheae of the fat-glands, whilst the 
cells figured by Stein are undoubtedly those of the fat-body, of 
which I give a figure (PI. XXYIII. fig. 15) for comparison. 
Sir John Lubbock (19), describing the corresponding glands 
in Coccus Cersicce , gives a totally different description. He 
says : — 
“ They are six in number, four large and two small, the latter 
being apparently attached by a short stalk to the peduncle of the 
large one which is furthest from the vulva. They lie three on 
each side, and their ducts open iuto the egg-canal close together 
and about halfway between the vulva and the division of the 
egg-canal into two oviducts. The internal structure is very 
distinct and interesting. It consists of many cells lying loose in 
the internal cavity, and resembling very much in form, size, and 
appearance the vitelligenous cells of the egg-follicle.” 
I have been unable to find any other published details on the 
structure of these glands, which I shall now give from my own 
observations. 
The gum-glands in the Blowfly are simple tubes, tortuous 
rather than convoluted, 2 m. in length, with an average dia- 
meter of T75 m. They have a glistening white appearance, 
and are beaded over the surface from the projection of the cells 
lining them. In sections these glands are seen to consist of an 
outer musculo-cellular coat, like the so-called peritoneal coat of 
the oviduct. This is lined by a single layer of large epithelial 
cells. The lumen is filled by a granular fluid or semifluid sub- 
stance. This is coagulated by alcohol, the granules suspended 
in it are blackened by osmic acid, and the intergranular material 
is scarcely stained by alkaline solutions of carmine. In this 
respect it differs entirely from the substance contained in the 
uterine pockets and from that with which the eggs are cemented 
together. 
The epithelial cells which surround the lumen of the gland 
are irregular in form and measure, on an average, 80 n in 
diameter, and from 30 to 40 /x in thickness. Many of these 
cells contain very remarkable spherical corpuscles, usually 
one in each cell (figs. 15 to 20). Besides these, some of the 
