Physiology of Trichodina pediculus. 417 
right side of the body. In an end view (fig. 13) of the animal, 
the vestibule narrows rapidly from its aperture to its bottom, 
whereas when seen in profile (fig. 8,v) the diminution of its 
diameter is more gradual. When the body is fully expanded, 
its aperture (m) is always open, and is circular, or broadly oval 
(fig. 12,m), in outline. This aperture lies just behind and ex- 
terior to the first spiral turn (fig. 11,5! to d®) of the vibratory 
margin of the cyathiform disk, and receives the termination 
(tig. 13, 5?) of that spiral within its depths. It might there- 
fore, with propriety, be designated as the internal prolongation 
of the disk. 
The anus (Pl. IX. figs. 12, 18, a@).—When the anus is open, 
which not unfrequently happens, it appears as a distinctly 
bounded, seemingly margined aperture, which lies very con- 
spicuously on the right side of the vestibule, and near its mouth. 
The esophagus (0, 0'), in conjunction with the vestibule (v), 
is an elongate-sigmoid (fig. 13) funnel-shaped cavity, which ex- 
tends obliquely backwards and across the body, nearly to its axis. 
When not in the act of taking in food, the cesophagus terminates 
in a fusiform point or pharynx, and may be recognized as a 
clear colourless space in the midst of the light-yellow tissue of 
the body. From the point where it joins the bottom of the 
vestibule it curves to the left, and thus forms the dorsal termi- 
nation of the sigmoid. In a profile view (fig. 8, 0,0!) it hes 
nearly parallel with the proximate or ventral surface of the 
body. When the pellets of food are forming, its posterior fusi- 
form termination (0!)—the so-called pharynx—gradually ex- 
pands into a globular cavity, which eventually exceeds in dia- 
meter the breadth of the mouth; but as soon as the food passes 
into the general digestive cavity, it assumes its accustomed 
funnel-shaped outlime. As has already been stated in the 
section on prehensile organs, it is lined by vibratile cilia, which, 
it may be added here, seem to cover its whole interior. 
The digestive cavity—Beyond the cesophagus there is no 
special cavity for the preparation or assimilation of food; the 
latter passes from the posterior end of the former through a 
simple expansible aperture directly into the general digestive 
cavity. The final assimilation of the food is accomplished, as in all 
other Vorticellidans, in a space which embraces every part of 
the body except that which is immediately occupied by the con- 
tractile vesicle (cv) and the reproductive organ (7). This space, 
therefore, serves both the purpose of a stomach and intestine ; 
nor does it appear to have any accessory glands or appendages 
of whatever kind that may assist in the process of digestion. 
The walls of the body, therefore, form the immediate parietes 
Ann. & Mag. N. Hist. Ser. 3. Vol. xvii. 27 
