OF THE PKOTOZOA. CILIATA. 279 



operation it continues to swim about, its appearance with the hall- swallowed 

 being is very curious. Again, when engulfed the anterior portion contracts, 

 whilst the posterior becomes dilated, gi^^ng the Enchelys a flask-shaped outline. 



In descriptions of the Ciliata, authors have used various terms, applied to 

 the segments or members of higher animals, to designate varieties in the form 

 and in the mutual relation and position of their parts. The application of 

 many of these terms to the Protozoa is indeed very arbitrary and fanciful ; 

 and it is only from the absence of better that we continue to emj)loy them. 

 The end of the body which advances foremost in swimming, and at which or 

 near to which the mouth is ordinarily placed, is called the head, and often has 

 an additional claim to the appellation by its construction as a segment distin- 

 guished by some points of structure from the rest of the body. The opposite 

 portion of the animal constitutes, when tapering or provided with some sort 

 of process, the tail, but is more generally spoken of, especially when not 

 distinguishable as a segment, as the posterior or caudal extremity. 



A ' dorsum ' or back, and a ' venter ' or abdominal surface, are usually de- 

 scribed, but are not readily determinable in aU genera, as, for instance, in the 

 VorticeUina and OpTirydina. To distinguish the one surface from the other, 

 regard must be had to the position of the mouth (which indicates the abdo- 

 minal surface), to that of the locomotive cilia and other processes, and to the 

 mode of progression. But, after all, the distinction will oftentimes be arbi- 

 traiy, and in consequence the description of a right and a left side frequently 

 so too. It is a general character of the Ciliata, that they are asymmetrical, 

 i. e. not formed of two equal and similar halves. An exception to this rule 

 exists in Coleps (XXIY. 284) and in the IchtJujdina (XXXI. 28-30), which 

 in Ehrenberg's system were included with the Rotatoria. Where, although 

 symmetry is not visible, a right and a left side are distingiushable, such Infu- 

 soria are called ' bilateral,' — e. g. the O.vytrlcMna (XXYIII. 10), Paramecimn 

 (XXIX. 25-30), CMlodon (XXIX. 48). 



Of minuter modifications in the figure of Protozoa, a large number have 

 found names which t\tl11 be best understood in the special structiu*al details of 

 particular animalcules. However, to mention some here used by Ehrenberg, 

 we may cite the frontal region or forehead — the obtuse or truncate part of 

 the head above the mouth ; the lips — projections above and below the mouth, 

 when this aperture is situated in a fissiu-e ; the tongue or palate, usually a 

 process in the oral fissure ; the rotary or ciliary disk, seen as a ciliated pro- 

 jectile process above the margin of the anterior extremity of the VorticeUina 

 (XXX. 1, 2, 9, 11, 14). In several genera the anterior portion of the body 

 is much produced, and looks like a long tubular neck or a tnmk, and hence 

 is called frequently by Ehrenberg proboscis, — e. g. in the genera Lacrymaria 

 (XXIV. 274, 275), Trachelius (XXIV. 287-289), Amphileptus, and Trache- 

 locerea (XXIV. 317-320). This term proboscis we have already seen used 

 to designate the long locomotive filaments or flabella of Phytozoa, totally 

 different processes from those called by the same name in the CiUata just 

 enumerated. Its use for one or the other should be set aside ; and although 

 at the best it conveys a very erroneous impression — for no such thing as a 

 proboscis or trunk, in the proper meaning of the word, has an existence in 

 any of the Protozoa — its application to these is less objectionable than to the 

 Phytozoa. In Uroleptus (XXY. 333) the posterior extremity is abniptly 

 elongated, and forms, according to the description of the same distinguished 

 naturalist, a tail. 



Consistence. — The Ciliata are composed principally of a very soft, almost 

 mucilaginous matter, which has been well named ' sarcode,'' since, like the 

 flesh or muscular tissue of higher animals, it seems to present an inherent 



