152 



BIOLOGY OF THE PROTOZOA 



motile organs of the ciliates, their stroke is not confined to one 

 plane but may be in any direction. This gi\'es to the Hypotrichida 

 an extreme \'ariety of movements unparalleled by any other group 

 of Protozoa. Many of them walk or run on the tips of their frontal 

 and ventral cirri (StylonycJiia) ; others swim with a peculiar jerky 

 movement (Aspidisea) ; others combine swimming due to the 

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

 cirri {Vronyckia, Euphtes, etc.). Such saltations are not limited 

 to the Hypotrichida, however, but are characteristic of organisms 

 in all groups where cirri are developed as in HaUeria r/rondinella 

 among Oligotrichida, Mesodinium cinctum among Holotrichida, etc. 



B 



Fig. 80. — .4, Onychaspis sp.; B, Onychaspis hcxeris. (Original.) 



In some cases cirri are said to be 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 instan- 

 taneous effect of a slight local irritation on a quietly resting Fleiiro- 

 nema chrysalis, for example, with its long cilia radiating out in all 

 directions, yet there are no cirri here. 



The synchronous and metachronous vibrations of cilia and cilia 

 aggregates, are probably regulated by coordinating fibers with 

 highl\' de\eloped irritability. This is the interpretation given by 

 Schuberg to the basal fibrils in the contractile zone of Paramecium 

 cavdatini'.; by Nerescheimer (1903) to certain fibers distinct from 

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



