886 The Poison-Apparatus of the Mosquito. 
past summer, however, gave me an opportunity of revising the 
subject, so that I have acquired some facility in finding and dis- 
secting the parts. I find that it is even easy to see the venomo- 
salivary duct from the outside, shining through the skin at the 
base of the head and neck in the undissected specimen. Also, 
thanks to the supervision of Professor Libbey and the manipula- 
tion of Dumas Watkins, of Princeton Histological Laboratory, I 
have been supplied with a set of excellent sections, which show 
the relations of the parts. One of these sections is here engraved 
in part (Fig. 1), exhibiting the insertion of the duct into the base 
‘of the hypopharynx, and its course below the nerve. I have 
also teased out and stained some of the glands, which have enabled 
me to show their structure and relations, as in Fig. 2. 
The secret was first discovered by an observation of fine drop- 
lets of a yellow, oily-looking fluid escaping from the apex of the 
hypopharynx (Fig. 1). I was then able to trace the course of 
this fluid down through the axis of the hypopharynx, its being 
divided in parts into droplets, and so indicating the tubular struc- 
ture of this organ. On examining the base of the hypopharynx I 
found it to be enlarged like the mouth of a trumpet, and provided 
with a sac-like reservoir, into which the end of a fine duct was 
inserted. Working backwards I saw the duct to be of the usual 
character of salivary ducts in the Diptera, but much finer than usual, 
. ` EE ates oi microms 
ing less tha 4 E: atar ipty. 
-in the house-fly.!' It is not readily identified by a low microscopl¢ 
power, and this may explain why it has not been previously detected. 
It has the usual chitinous lining, surrounded by the nucleated hype” 
dermis which secretes it, transversely'striated as in trachese (Fig. Hi 
but it is distinguished from the tracheæ by the comparative smal 7 
ness and constancy of its diameter, and by the absence of ramifica- 
tions. It runs back in the lower part of the head, beneath the 
nervous commissure (n in Fig. 1), for two-fifths of a millimetre 
In the throat it bifurcates, its two branches being each as long 
the undivided segment, and running on the right and left of t 
nerve-cord into the prothorax, where they terminate in glands 0. 
characteristic structure, 
DOVU 
1A microm is one-thousandth part of a millimetre, or one-twenty- 
five-thousandths of an inch. 
