STRUCTURAL DIFFERENTIATIONS 147 



suis, see p. 108), and center in a specialized neuromotor bod}-, the 

 motorium (Yocom, Taylor, Sharp). 



In some cases cilia are uniform in length over the entire body 

 {OiKilina) ; in other cases they are longer in the region of the mouth 

 or around the posterior end, but no sharp dividing point separates 

 short from long ones (Fig. 75). In some cases they are uniformly 

 long and vibrate like flagella (Actinobohis radians, Fig. 81, p. 154). 



4. Composite Motile Organs.-" A well-marked characteristic of 

 cilia is the ability of two or more to fuse into motile organs of vari- 

 able complexity. Such combinations give rise to membranulae, 

 membranelles, undulating membranes and cirri, each of which, 

 although composed of fused cilia, originates or grows as an inde- 

 pendent and complete organoid. In each case also the component 

 cilia may be demonstrated by use of dilute alkalies such as potas- 

 sium or sodium hydrate. 



Membramilce.—Memhriimilis are xery long, delicate, finely-pointed 

 aggregates of cilia which differ from the somewhat similar cirri 

 in moA'ement and in composition, while their basal granules, in 

 Didinium nasidvm at least, are connected with the vicinity of the 

 nucleus by definite rhizoplasts (Fig. 89, p. 180). Similar membran- 

 ulse form the basal ring in Vorticellidae (Schroder, Schuberg, etc.). 



Membranelles.— ^lemhraneWes are formed by the fusion of cilia 

 in the region of the mouth. In many of the Holotrichida the cilia 

 are longer just posterior to the mouth than in other regions of the 

 body, frequently forming circlets about the mouth as in Lacrymaria 

 olor or L. lagenida (Fig. 76) . In the other Orders of Ciliata oral cilia 

 are fused to form membranelles. In the oral regions the body is 

 usually differentiated into a specialized food-collecting, frequently 

 funnel-like structure called the peristome. Cilia on the floor of the 

 peristome are usually longer than in other parts of the body, and in 

 four of the five orders of ciliates some of these are invariably aggre- 

 gated in triangular, quadrilateral or ribbon-like membranelles and 

 membranes for producing food-bringing currents of water toward 

 the mouth. In every order except the Holotrichida a fringe of 

 such specialized motile organs, known as the adoral zone, lies on the 

 left margin of the peristome (Fig. 78). 



]Membranelles are usually made up by the fusion of two rows of 

 cilia as shown by the double row of basal bodies (^Nlaier) and their 

 flat or curved faces make powerful sweeps in the water (Fig. 78, 

 p. 150). According to Schuberg, Gruber, Maier and others, the 

 anchorage of these organoids is quite complex. The basal granules 

 form a double row immediately below the periplast; fibrils from 

 these, analogous to rhizoplasts, form a broad triangular basal 

 plate and are then brought together to form an end thread which 

 connects the membranelle with coordinating fibers (Fig. 57, p. 110). 



