POLYGASTIUA. 



11 



The genus Slentor (Jig. 8) contains some of 

 the largest and most active animalcules be- 

 longing to the class, and, as might be expected, 

 these are amongst the most conspicuous for the 

 perfection of their locomotive organs. These 

 beautiful creatures resemble gelatinous trum- 

 pets, the bodies of which are flexible and con- 

 tractile in all directions, either while swimming 

 about freely in the water, or while attached, as 

 they frequently are, to some foreign body by 

 means of a little sucking disc which terminates 

 the pointed extremity of the tail. 



The whole of the trumpet-shaped body of 

 Stentor is covered over with innumerable cilia, 

 disposed in regular rows, and of sufficient size 

 to be easily distinguishable by the microscope. 

 Its broad end is terminated by a circular disc, 

 the diameter of which is considerably larger 

 than the widest part of the body. The entire 

 surface of this disc is likewise covered with 

 multitudes of cilia, arranged in regular con- 

 centric circles; and, moreover, its margin is 

 fringed all around with a single row of cilia of 

 larger dimensions, which by the- rapid succes- 

 sion of their movements give the appearance of 

 a wheel spinning rapidly round, and by its 

 revolution causing powerful currents in the sur- 

 rounding water. At the lower part of the 

 margin of the ciliated disc the ciliary zone 



Fig. 8. 



turns inwards, forming a spiral fold around 

 a funnel-like aperture (fig. 8) which leads to 

 the mouth, and likewise lodges the orifice 

 through which digested materials are cast out. 

 The currents caused by the marginal fringe 

 around the disc are all directed towards the 

 oral aperture, and consequently, by bringing 

 nutritive particles to the mouth, this part of 

 the apparatus becomes eminently subservient 

 to nutrition. In several species of Stentor, in 

 addition to the apparatus of cilia described 

 above, there is an additional riband-shaped 

 band of these vibratile organs extending from 

 near the mouth to a considerable distance 

 towards the hinder part of the body, the outline 

 of which has an undulated appearance. 



The Trichodinae, or Urn animalcules, have 

 no pedicle or elongated tail, but are provided 

 with a fasciculus or circlet of cilia situated in 

 front of their bodies, which are disc-shaped, 

 bowl-shaped, or conical, the mouth being ap- 

 parently a single orifice situated in the ciliary 

 circlet. One species of this group, T. pedicu- 

 kis, seems to be parasitically attached to the 

 Hydra viridis, and allied forms have been met 

 with in the respiratory laminee of several bi- 

 valve shell-fish, ( Anodonta, Unto, &c.,) and 

 also in Gyrodactylus coronatus, itself a parasite 

 inhabiting the gills of the Crucian Carp fCy- 

 prinus Caras&ius). That these animalcules are 

 really Polygastrica, and not sterelminthous en- 

 tozoa, Ehrenberg satisfied himself by feeding 

 them with indigo. Urocentrum seems to be 

 similarly organized, only it is furnished pos- 

 teriorly with a sharp style-like process. 



But perhaps the most remarkable as well as 

 most elegant of all the forms of animalcules 

 belonging to this group are the Vorticcllte, 

 Cfig-9,} the sight of which cannot fail to exact 

 the untiring admiration of the microscopical 



Stentor Roeselii, highly magnified, 

 t, viscus supposed by Ehrenberg to be the testis. 



Vorticdla cyatldna. 



b, c, d, e,f, exhibit the various steps of fissiparous 

 reproduction in this animalcule. 



