36 INFUSOEIA. 



membrane that had previously confined it, the filament unrolling itself 

 so quickly that the eye can scarcely follow it, until it ultimately lies 

 straight and rigid on the field of the microscope, looking like a very fine 

 and long acicular crystal. 



(72.) This remarkable filament, when completely evolved, consists 

 of two portions a rigid spiculum-like portion, acutely pointed at one 

 end, and continuous at the opposite end with the second portion, which 

 is in the form of an excessively fine filiform appendage, less than 

 half the length of the spiculum. This second portion is generally seen 

 to be bent at an angle on the first, and is frequently more or less curved 

 at the free end. The form of the evolved trichocysts is best observed 

 in such as have floated away towards the margin of the drop of water 

 and are there left dry by the evaporated fluid. In many of them the 

 filiform appendage is not visible, and they then merely present the 

 appearance of a simple, long, fusiform spiculum. 



(73.) Few subjects have afforded a more fertile field for discussion 

 than the internal organization of these almost invisible creatures ; and 

 even at the present moment many points of their economy are by no 

 means satisfactorily elucidated. The remoteness of their structure from 

 that of the higher animals, and a natural mistrust felt by recent ob- 

 servers in the capabilities of the instruments placed at their disposal, 

 gave rise at first to doubts and hesitation, which no longer exist. 



The digestive apparatus of the Infusoria was originally described 

 by Ehrenberg as consisting of a number of internal sacculi, varying 

 from four to two -hundred in number in different species. These 

 sacs were stated by that indefatigable microscopist to be readily distin- 

 guishable without any preparation, but capable of being rendered 

 more conspicuous by feeding the animalcules with pure carmine or 

 indigo, the coloured particles of which substances they eagerly swallow. 

 In one large division, called AKENTEEA, the sacculi or stomachs were said 

 to arise by separate tubular pedicles from the mouth itself (fig. 16, l); 

 whilst in others (ENTEEODELA) there was supposed to be a complete 

 intestinal canal, terminated by a mouth and anus, to which the sacculi 

 or stomachs, as they were called, are appended : sometimes the intestinal 

 canal is stated by the same authority to form a circle in the body 

 ANOPISTHIA, Ehrenb.), as in the Vorticella (fig. 16, 2) ; or else the mouth 

 and anus are placed at opposite extremities of the body, through which 

 the intestinal tube passes either in a straight course, or exhibiting 

 several flexuous curves in its passage (ENANTIOTEETA and ALLOTEETA, 

 Ehren.) (fig. 16, 3 and 4). When neither the mouth nor anus is ter- 

 minal, such animalcules belong to the group denominated KATOTEETA 

 by the same author. 



(74.) However imposing, from their completeness, the views of 

 Ehrenberg concerning the digestive system of the polygastria may be, 

 and sanctioned as they have been by almost general consent, we cannot 



