GLAND STRUCTURE. 
115 
(^) which curve upwards and wind round the optic 
ganglion on each side of the head. Along the 
whole length, surrounding the duct to its blind end, 
are situated round or unequally shaped bag-like small 
granulations, composing the substance of these glands, 
called acini^ and containing cells. The duct consists 
of a strong transparent tube, which is considerably 
thickened as it approaches the knee-shaped opening, 
and is from to -g inch in diameter. The cells 
in the acini, which are surrounded by the membrane 
{propria) through which the blood passes, produce the 
secretion. 
Schiemenz (144) says these are intracellulai% and 
that every part of the surface of each cell is absorbent. 
The secretion is conducted through ducts o'oo2 mm. 
diameter, which enter each of the cell walls. After 
leaving the cells, they pass through a tube, where, by 
a sieve-like opening (c, n\ they enter the main duct 
(c, i). The acini contain a variable number of cells 
(c, /^), and Schiemenz found some with only one (c, /). 
They are very large in young bees (nurses), well filled, 
yellowish white ; but the cell walls, although per- 
ceptible, are indistinct. In older workers the acini 
are very much shrunken, mulberry-shaped, yellow, and 
the cell walls cannot be recognised. The whole 
gland is surrounded by the outer membrane (propria), 
and the secretion from it is acid. 
This gland is not developed either in the queen or 
drone. In the latter there is not the slightest trace of 
it, the hypo-pharyngeal plate having no perforations. 
On this plate in the queen the perforations are very 
