The intestine which traverses the interior of the body in all the higher forms of polygastric animalcules, and connects all the internal sto machs with its cavity, presents very different appearances in different genera and even in different species of the same genus. In the vorticella citrinu (fig. 4 II) the intestine (fig. 4 B, b, c) passes downwards from the mouth, nearly of equal width throughout, and after forming a curve in the lower part of the body, it ascends to terminate at the same oral funnel shaped ciliated aperture, (fig. 4 B, a,) between tine pursuing the same circular course through the body, is sacculated or irregularly dilated into round vesicles throughout its whole length, and from these enlarged parts the little stomachs commence by short narrow necks. In other species of the stentor the intestine is twisted in a spiral manner throughout its circular course. Many of the polygastric animalcules which ap proach nearer to the helminthoid classes in the lengthened form of their body, have the mouth and anus placed at the opposite extremities, as in these higher classes. In the long body of the enchelis pupa, (fig. 6,) the intestine is seen passing straight and cylindri cal through the body from the wide ciliated terminal mouth (fig. 6, a) to the opposite dilated anal termi nation (fig. 6, b) and giving off numerous small sacs along its whole course. Such animalcules form the group termed orthocala from this straight course of the intestine. The intestine, however,in the leucophrys patula (fig. 5 A) passes in a spiral course through the short and broad body of the animalcule, giving off small stomachs or coca along its whole course, and such crooked forms of the alimentary canal com pose the group of campylacala, in the distribution of this class proposed by Ehrenberg.
Thirty-five genera of polygastrica present an intestine passing through their transparent body, and developing from its parietes these minute globular cceca, which have been regarded as stomachs, from the quickness with which the animalcule conveys the food into them, and from its not accumulating or retaining its food in any other part of the digestive apparatus. More than a hundred of these stomachs have been seen in the paramecium and aurelia filled at the same time, and there may have been many more unseen from their empty and col lapsed state. These little sacs are contracted, filifonn, and almost invisible, when empty; but they are susceptible of great dilatation, and are sometimes seen filled with water or dis tended with smaller animalcules seized as food. Viewed through the microscope these minute animals present very different appearances, ac cording to the quantity and kind of food con tained in their meal appendices, and from this circumstance twelve different species of animal cules, belonging to six supposed distinct genera, have been formed of the single vorticclla con vallaria. No glandular organs to assist in digestion have been observed in the polygastric animalcules ; and notwithstanding their almost invisible minuteness and the great simplicity of their structure, they appear to be the most numerous, the most active, the most prolific, and the most voracious of all living beings.
Very recently, by the aid of an improved mi croscope made at Berlin, Ehrenberg has been able to detect a dental apparatus in the kolpoda cucullulus of Muller, one of these minute poly-. gastric animalcules, which shews a further ana logy between them and the helminthoid articu lata. Notwithstanding the number of stomachs in this class of animals, and the infinite variety of prey which commonly surround them, we often observe them devouring animals, which from their magnitude are incapable of being conveyed into these cavities. I have observed a trachelius, after swallowing several monads which swarmed around it, proceed slowly to swallow down a trichoda, which appeared to be ten times the size of one of its internal sacs. It took about a minute to swallow the trichoda, after having turned it in different directions with its long transparent moveable upper lip. The prey could not be perceived to offer the slightest resistance, while the trachelius, with its upper lip spread over the small anterior end of the trichoda, gradually advanced and ex panded the short lower lip to embrace it below. The body of the trachclius was much shortened during this prolonged act, being drawn forwards towards the lips, and the animalcule, become slower in its movements, was sensibly distended on one side by this large prey in the intestine ; but in less than half an hour it had recovered its usual lengthened form and gliding move ments, and was seen to seize again the smaller monads around it. Ehrenberg has figured an enchclys swallowing a loxodes ten times the size of its stomachs even when filled with car mine, and in the body of the loxodes he has represented navicule which have been swal lowed, though several times the size of any of its stomachs distended with sap-green. In the capacious alimentary cavity of the paramecium chrysalis I have found a constant slow revolu tion of the whole contents, like the cyclosis in the large cells of a chara, and the round sacs appear often to be driven to and fro like loose balls in a sac. Baron Gleichen has figured some of these round sacs of Ehrenberg separate from the animalcules, as a bolus of matter which had escaped per arum. These round transparent bodies are often hurried to one end of the animalcule's body and then to the oppo site, or spread generally through the cavity, and they sometimes join partially in the general internal cyclosis of the abdominal cavity. In many genera of polygastric animalcules a cir cular proboscis is seen around the mouth, composed of long parallel straight teeth closely applied to each other, which can be extended or retracted, and forms their masticating appa ratus.
(For the higher forms of the alimentary canal in all the separate classes of the animal king dom, see the names of the several classes from the PORIFERA to the 1\1 A AI M ALI A, ANIMAL KINGDOM, and the preceding article DIGES TION.) (R. E. Grant.)