AND PHYSIOLOGY OF TRICIIODINA. 125 



and forming it into pellets at the bottom of the oesophagus and its passage into the general 

 cavity of the body may be seen at any time, and without any particular preparation. On 

 this account it is no difficult task to ascertain the position of the mouth, and the trend of 

 the vestibule and oesophagus, as well as the posterior termination of the latter. 



The vestibule (v) is as distinct from the oesophagus (o) as in most of the Vorticellida?. Its 

 aperture (m) is very broad, and diverges almost insensibly into the peristome (d). It 

 passes into the body in a direction which is in strict continuation (fig. 13) with the spiral 

 trend of the border (d) of the disc; that is to say, it winds posteriorly, dorsally, and 

 toward the 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 exterior to the first spiral turn (fig. 11, J 1 to d fj ) of the 

 vibratory margin of the cyathiform disc, and receives the termination (fig. 13, b 2 ) of that 

 spiral within its depths. It might, therefore, with propriety, be designated as the internal 

 prolongation of the disc. 



The anus (figs. 12, 13, a). When the anus is open, which not unfrequently happens, 

 it appears as a distinctly bounded, seemingly margined aperture, which lies very conspicu- 

 ously on the right side of the vestibule, and near its mouth. 



The oesophagus (o, o 1 ), in conjunction with the vestibule (v), is an elongate sigmoid (fig. 13), 

 funnel-shaped cavity, which extends obliquely backwards and across the body, nearly to its 

 axis. When not in the act of taking in food, the cesophagiis terminates in a fusiform point, 

 or pharynx, and may be recognized as a clear, colorless 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 termination of the sigmoid. In a profile view 

 (fig. 8, o, o 1 ) it lies nearly parallel with the proximate or ventral surface of the body. 

 When the pellets of food are forming, its posterior fusiform termination (o 1 ) — the phar- 

 ynx, so-called — gradually expands into a globular cavity, which eventually exceeds in 

 diameter the breadth of the mouth ; but as soon as the food passes into the o-eneral 

 digestive cavity, it assumes its accustomed funnel-shaped outline. 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 oesophagus 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 assimi- 

 lation 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 contractile 

 vesicle (cv) and the reproductive organ (»). This space, therefore, serves both the purpose 

 of a stomach and intestine ; nor does it appear to have any accessory glands or append- 

 ages of whatever kind, that may assist in the process of digestion. 



The walls of the body, therefore, form the immediate parietes of the digestive cavity. 

 There are, at least, two of these walls. The inner one (p 1 ) consists of a clear, amber- 

 colored, homogeneous, formless tissue, in which all the organs are imbedded. The other, 

 or exterior ivall (p), embraces the inner one like a film, and has more of the character of a 

 colorless excretion than a true tissue. It is thickest about midway between the two ends 

 of the body, and gradually thins out to an inconspicuous stratum at the anterior and 



MEMOIRS DOST. SOC. NAT. HIST. Vol. I. 32 



