Dicranura vinula, and other Notes. 119 
while but a single retractor (7 1 *) is attached to the apex 
of ¢?, a second, however, being attached to this tube at 
a point about half-way along its length (7 m*'). These 
tubes are lined with chitin of the ordinary kind covering 
the external surface of the body, but towards their ex- 
tremities are provided with a number of fine needle-like 
bristles, arising in tufts from the summits of low knobs 
(vide Figs. 1 and 3). ‘Their epithelia have none of the 
usual characters of glandular cells, and I am confident 
that they are not of this nature. I can form no positive 
opinion of the function of these eversible tubes. 
Schiitfer (19) suggests that these side pouches are 
reservoirs for the acid, and that the bristles serve to keep 
the tubes from being crushed by the body-fluids pressing 
upon them. It seems to me unlikely that such relatively 
small structures should be the reservoirs for so large a 
gland, whose own internal capacity appears ample for the 
purpose; nor am I convinced that these tubes do as a 
matter of fact ever contain acid. It seems highly im- 
probable that they are of any service in the discharge of 
the formic acid, for they are not everted by the larva 
unless external pressure is put upon its body, and even 
then not until the acid has been already discharged. This 
at least is my experience, and Professor Poulton in con- 
versation confirms me, though Klemensiewicz (8) asserts 
that they are everted just before the discharge. It is 
possible that they may be of service in dire necessity 
when the larva is seized by a foe in somewhat increasing 
the terrifying aspect of the victim, and affording a some- 
what larger surface for the evaporation of the formic acid 
in close proximity to the aggressor. There are no pro- 
tractor muscles to these tubes, their eversion being solely 
due to pressure of liquid. 
The vestibule itself is provided with powerful protractor 
and retractor muscles. ‘lhe former are situated along the 
anterior side of the vestibule on either side of the median 
region from which they are absent; they are inserted 
about half-way up the side of the vestibule and take 
origin from the internal surface of the body wall anterior 
to the slit aperture; on each side, right and left, these 
muscles form an almost continuous sheet, which can, 
however, be separated into some five or six main bundles 
which are visible to the naked eye (vide Figs. 1 and 4, 
pmv). These muscles come into action prior to the 
