DIGESTIVE CANAL. 



29 



disposition of their alimentary cavities; but 

 however long they remain in these coloured 

 infusions, with their stomachs distended with 

 the colouring matter, it is not perceived to 

 communicate the slightest tinge to the general 

 cellular tissue of their body. ~ In most of the 

 animals of this class there is an alimentary 

 canal with an oral and an anal orifice, which 

 traverses the body and is provided with nume- 

 rous small round coecal appendices, which open 

 into its sides throughout its whole course, and 

 which appear to perform the office of stomachs 

 in receiving and preparing the food. In the 

 simplest forms of animalcules however, (as in 

 the monas atomus represented in Jig. 4 A) there 



Fig. 4. 



is but one orifice (fg. 4 A, a) to the alimen- 

 tary cavity, and the numerous coecal appendices 

 (/g.4 A, b} open into this general wide orifice 

 placed at the anterior extremity of the body. 

 This simpler form of the digestive apparatus 

 is found in the monads and in about forty other 

 known genera of polygastrica, which, from 

 this circumstance of their having no intestine 

 passing through their body, have been grouped 

 together as an order under the name of anen- 

 tera. In the monas termo, which is only 

 about the two-thousandth of a line in diameter, 

 four and even six of these roand stomachs have 

 been seen filled with the colouring matter, 

 although they did not appear to be half the 

 number which might be contained in its body. 

 Each of these round stomachs was about ^ of 

 a line in diameter, and they appear to open, 

 as in other anentera, by a narrow neck into a 

 wide funnel-shaped mouth surrounded with a 

 single row of long vibratile cilia, which attract 

 the floating organic particles or minuter invisi- 

 ble animalcules as food. This anenterous form 

 of the digestive sacs is found both in the lori- 

 caled and in the naked kinds of animalcules 

 belonging to the lowest genera of the class, 

 many of which, however, have been found to 

 be only the young of supposed higher genera. 



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 citrina (jig. 4 B) the intestine (Jig. 

 4 B, b, r) 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, (Jig. 4 B, a,) between 



the two circles of cilia around the head at 

 which it commenced, having numerous coecal 

 stomachs communicating with its cylindrical 

 equal canal throughout its whole course. This 

 circular form of intestine opening at both its 

 extremities in the same ciliated aperture, is 

 seen also in the carchesium, zoocladtum, episty- 

 lis, ophrydium, vaginicola, and other genera, 

 which from this character are termed cyclocala. 

 In some of the animalcules of this group, as in 

 the stentor polymorphus, (jig. 5 B,; the intes- 



Fig. 5. 



Fig. 6. 



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, (Jig. 6,) the intestine is 

 seen passing straight and cylindri- 

 cal through the body from the wide 

 ciliated terminal mouth (Jig. 6, a) 

 to the opposite dilated anal termi- 

 nation (Jig. 6, 6) and giving off 

 numerous small sacs along its whole 

 course. Such animalcules form the 

 group termed orthoccela from this 

 straight course of the intestine. The 

 intestine, however, in the leucophrys 

 patula (Jig. 5 A) passes in a spiral 

 course through the short and broad 

 body of the animalcule, giving off 

 small stomachs or coeca along its 

 whole course, and such crooked 

 forms of the alimentary canal com- 

 pose the group of campyloccela, 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 paramtEcium 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, 



