M. T. Thorell on the Morphology of the Argulide. 157 
the front, whence I conclude that both borders of the lower 
lip have coalesced with each other in the formation of the 
mouth-tube. Above, before the middle of the front surface, 
two small teeth are observable. Laterally, its diameter is 
almost the same throughout ; and the club-like shape depends 
consequently on the fact of its being somewhat broader at the 
extremity. The tip itself is obliquely truncated, and shows 
behind a hood-like extension of the wall of the tube, which 
spreads itself over the back part of the oral aperture in the 
form of a large, moveable, almost crescent-shaped lip. The al- 
most triangular oral aperture is bounded by the two posterior 
(inferior) arms of an almost H- or X-shaped chitinous structure 
or apparatus, as also by two thin, oblong, chitinous lamelle, 
which are rounded at the extremity, and are situated immedi- 
ately beneath these, and whose direction is parallel with them : 
on the inner margin these latter show some few saw-like teeth. 
Both these lamelle I regard as maxille. 
Somewhat higher up in the tube are placed the two man- 
dibles. They are oblong, almost triangular, somewhat curved, 
and end on either side in a finely poimted apex, above and be- 
fore which the convex (lower and inner) margin is raised into 
two smaller and two stronger teeth. These mandibles are di- 
rected with their tips towards each other, inwards and upwards, 
in the gullet, while the maxille diverge backwards and out- 
wards. 
In order to give suppleness to this armature, and at the 
same time to support the mouth-tube itself, this last contains a 
rather complicated chitinous framework. Such a framework is 
apparent on either side of the tube, and involved in its wall, 
being somewhat thickened beneath the crescent-shaped lp, 
where it forms a knob on either side of the tube. This knob 
furnishes the principal support for the mandible. Two other 
such chitinous processes, which are placed more inwards and 
backwards in the tube and do not touch its walls, extend below 
the lip, whose arch they seem to support, and form here a bow 
by means of which they unite with the two side processes. The 
X-shaped chitinous framework which bounds the oral aperture 
is also brought imto connexion with these processes by means 
of its arms, and thus, at the extremity of the mouth-tube, is 
formed a solid apparatus. 
The gullet ascends as a slender, strongly chitinous tube, and 
proceeds backwards in a bowed shape through the nervous 
ring situated in the throat to the stomach, where it opens, by 
means of a remarkable cup-like organ, into a cardia or stomach- 
mouth (‘ mag-mun’’), which probably acts as a sucking-pump. 
I think it probable that the maxille serve to effect an opening 
