774 



MICROSCOPIC FORMS OF ANIMAL LIFE 



aperture (fig. 593, A, B), or are limited to some one part of it, 

 which is always in the immediate vicinity of the mouth, sup- 

 plies the means in this group of Infusoria both for progres- 

 sion through the water and for drawing alimentary particles into 

 the interior of their bodies. In some their vibration is constant, 

 whilst in others it is only occasional. The modes of movement 

 which infusory animalcules execute by means of these instru- 

 ments are extremely varied and remarkable. Some propel them- 

 selves directly forwards, with a velocity which appears, when highly 

 magnified, like that of an arrow, so that the eye can scarcely follow 



them ; whilst others drag their 

 bodies slowly along like a leech. 

 Some attach themselves by one 

 of their long filaments to a fixed 

 point, and revolve around it with 

 great rapidity, whilst others 

 move by undulations, leaps, or 

 successive gyrations : in short, 

 there is scarcely any kind of 

 animal movement which they 

 do not exhibit. But there are 

 cases in which the locomotive 

 filaments have a bristle-like firm- 

 ness, and, instead of keeping 

 themselves in rapid vibration, are 

 moved (like the spines of Echini) 

 by the contraction of the integu- 

 ment from which they arise, in 

 such a manner that the animal- 

 cule crawls by their means over 

 a solid surface, as we see espe- 

 cially in Trichoda lynceus (fig. 

 FIG. 593. Group of Vorticella nebuhfera ^07 -p c\\ T mi^T 



showing, A, the ordinary form ; B, the D * 7 > *> **)\ in bMtOOfm and 

 same with the stalk contracted ; C, the AflUftMa, again, the mouth IS pro- 

 same with the bell closed ; D, E,F, sue- v id ec [ w jth a circlet of plications 

 cessive stages of fissiparous mulbplica- Qr foldgj looking Ufc/fcfc^ 



which, when imperfectly seen, re- 

 ceived the designation of ; teeth ; ' 



their function, however, is rather that of laying hold of alimen- 

 tary particles by their expansion and subsequent drawing together 

 (somewhat after the fashion of the teiitacula of zoophytes) than of 

 reducing them by any kind of masticatory process. Some, like 

 Opalina, are entoparasitic, and have no mouth ; a form allied to 

 Opalina (Anoplophrya circulans) lives in the blood of Asellus 

 aquations; other entoparasites, such as TncJtonympha in the ' white 

 ant,' still possess their mouth. The curious contraction of the foot- 

 stalk of the Vorticella (fig. 593), again, is a movement of a different 

 nature, being due to the contractility of the tissue that occupies 

 the interior of the tubular pedicle. This stalk serves to attach the 

 bell-shaped body of the animalcule to some fixed object, such as a 

 leaf or stem of duck-weed and when the animal is in search of 



