74 THE VITAL FUNCTIONS. 



for some continue long in a contracted state, so as not to be 

 visible; while, at another time, they readily admit the co- 

 loured food. It is, therefore, only by dint of patient watch- 

 ing that the whole extent of the alimentary tube, and its 

 apparatus of stomachs, can be fully made out. Fig. 255, 

 above referred to, exhibits the Leucophra patula of Ehren- 

 berg,* with a few of its stomachs filled with the opaque par- 

 ticles: but Fig. 256 shows the whole series of organs as it 

 would appear if it could be taken out of the body, and placed 

 in the same relative situation with the eye* of the observer, 

 as they are seen in the first figure. In some species, from 

 one to two hundred of these sacs may be counted, connected 

 with the intestinal tube. Many of the larger species, as the 

 Hydatina senta, exhibit a greater concentration of organs, 

 having only a single oval cavity of considerable size, situated 

 in the fore part of the body. In the Rotifer vulgaris, the 

 alimentary canal is a slender tube, considerably dilated near 

 its termination. In some Vorticdlse, the intestine, from 

 which proceed numerous caeca, makes a complete circular 

 turn, ending close to its commencement: Ehrenberg forms 

 of these the tribe of Cycloccela, of which the Vorticella cit- 

 rina, and the Stentor polymorphus, are examples. Thus 

 do we discover the same diversity in the structure of the 

 digestive organs of the several races of these diminutive be- 

 ings, as is found in the other classes of animals. 



The Hydatina senta, one of the largest of the infusoria, 

 was found by Ehrenberg to possess a highly developed 

 structure with respect to many systems of organs, which we 

 should never have expected to meet with so low in the 

 scale of animals. As. connected with the nutritive func- 

 tions, it may here be mentioned that the head of this ani- 

 malcule is provided with a regular apparatus for mastica- 

 tion, consisting of serrated jaws, each having from two to 

 six teeth. These jaws are seen actively opening and shut- 

 ting when the animal is taking its food, which consists of 



* Trichoda patula. Muller. 



