DERIVED ORGANIZATION— TAXONOMIC STRUCTURES 161 



movement (Aspidisca) ; others combine swimming due to the 

 adoral zone with sudden jumps or springs due to the anal or caudal 

 cirri (Uronychia, Euplotes, etc.). Such saltations are not limited 

 to the Hypotrichida, however, but are characteristic of organisms 

 in all groups where cirri are developed as in Halteria grandinella 

 among Oligotrichida, Mesodinium cinetum among Holotrichida, etc. 

 In some cases cirri are differentiated as tactile organs, especially 

 the more dorsal ones of certain Hypotrichida. It is probable that 

 such cirri are no different from other motile organs of the ciliates 

 in this respect, extreme irritability being a common characteristic. 

 Few observers can have failed to note the instantaneous effect of 

 a slight local irritation on a quietly resting Pleuronema chrysalis, 

 for example, with its long cilia radiating out in all directions, yet 

 there are no cirri here. 



Fig. 90. — Two species of Aspidisca. (Original.) 



The synchronous and metachronous vibrations of cilia and cilia 

 aggregates are probably regulated by coordinating fibers with 

 highly developed irritability. This is the interpretation given by 

 Schuberg to the basal fibrils in the contractile zone of Paramecium 

 caudatum; by Neresheimer (1903) to certain fibers distinct from 

 the myonemes in Stentor coerulens, and by Sharp, Yocom, Taylor 

 and others, to conspicuous fibers in Diplodinium ecaudatum and 

 Euplotes patella (see p. 127) ; others, however (e. g., Jollos, and Belaf ), 

 interpret them as supporting structures. In the latter organism 

 Yocom (1918) and Taylor (1920) found fibers running from the 

 posterior anal cirri and from the adoral zone of membranelles to a 

 common anteriorly placed structure termed the motorium, which 

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