POLYGASTRICA. 



ratus of radiating muscular fibres, to the successive contractions of 

 which the rotation of the cilium is owing. Such an arrangement 

 is, to say the least, hard to be conceived, for in this case we must 

 attribute to these acrite beings an elaboration of structure of infi- 

 nite complexity ; and in creatures so small, how can the human 

 mind imagine the cilia to be wielded by many millions of distinct 

 and independent muscles, as such a supposition would infer ? 

 Some authors attempt to get rid of the difficulty by ascribing the 

 apparent ciliary movement to the rapid undulations of mem- 

 branous fins ; others altogether deny its existence, asserting that 

 the vibratory appearance is caused by the mingling of some secre- 

 tion which exudes from the surface of the animalcule with the sur- 

 rounding fluid, in the same manner as the union of spirit of wine 

 and water gives rise to an oscillation of particles visible to the 

 naked eye : to these suppositions, however, we barely allude, be- 

 cause we are convinced that any one who with a good microscope 

 and an unbiassed mind investigates the subject, will be con- 

 vinced that the cilia are such as we have described above, 

 however unable he may be to conjecture the cause of their 

 movement. 



(79.) The mouth of the polygastrica is generally a simple and 

 extremely dilatable orifice, and, with a few rare exceptions, is un- 

 provided with any masticating organs ; yet in Nassula elegans, 

 (Jig- 17, 1,) and a few kindred species, Ehrenberg describes a 

 dental system of a most extraordinary description : this consists of 

 a prominent cylinder (a), of which an enlarged view is given at , 

 composed of numerous long teeth adapted to seize and bruise 

 materials used as food. 



(80.) The digestive apparatus itself, from the peculiarity of its 

 structure, has given the character usually employed to distinguish 

 the entire class : it is described as consisting essentially of a 

 number of internal sacculi, varying from four to two hundred in 

 number in different species. These sacs are readily distinguishable 

 without any preparation, but are 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 A NEXT ERA, the sacculi or stomachs are said 

 to arise by separate tubular pedicles from the mouth itself 

 (./? 18, 1); whilst in others, ENTERODELA, there is supposed 

 to be a complete intestinal canal, terminated by a mouth and 

 anus, to which the sacculi or stomachs, as they are called, 



