212 Mr Harrison, ‘A preliminary account of the 
By contraction of the four protractor muscles, the rigid buccal — 
plate is impelled forwards, and everts the mtegumentary folds 
already mentioned as lying dorsally and laterally about the mouth 
opening, so that a small hood-shaped projection, open ventrally, is 
formed in front of the head. This is the haustellwm of the older 
writers. In the process of eversion, the teeth on the dental — 
plates are revolved outwards, and not only effect a superficial 
fixation of the parasite upon the skin, but also, owing to their 
diverging paths, tightly stretch the skin. It should be noted that, 
since this haustellum is open on the ventral side, it cannot form a ~ 
closed chamber when in contact with the skin of the host, as is 
generally assumed. On relaxation of the protractors, and con- 
traction of the retractors, the buccal plate 1s drawn backwards, 
and the haustellum. disappears. 
The ventral portion of the buccal cavity 1s somewhat expanded 
laterally throughout its length, and the cavity is a little wider 
posteriorly than anteriorly. 
The pumping-pharyne. 
The pumping-pharynx les between the cornua of the buccal 
plate, projecting somewhat behind their hinder ends. The cornua 
are in this region bent downwards (Fig. 5) so as to partly surround, 
above and at the sides, two lateral cavities which are part of the 
Fig. 5. Transverse section through pumping-pharynx about the middle 
of its length. Diagrammatic. 
pumping-pharynx, but which are almost completely cut off from 
it in the resting condition. In this condition the pumping- 
pharynx resembles an early gastrula, or a collapsed rubber ball, of 
which the upper half has been pushed down into the lower. A 
large number of dilatator muscles (Figs. 4, 5, Plate VI, Fig. 1, 
dpp.) are inserted into this depressed roof, which run to the dorsal 
