346 University of California Publications. [Zoology 



by secondary ridges one-half the height of the primary. These 

 are ectoplasmic strnctnres and disappear when the animals are 

 treated with killing and fixing reagents. There is but a single 

 row of the polygonal areas between the primary ridges at the 

 anterior end of the animal. At the middle where these ridges 

 are farthest apart there is a double row of these areas, and at the 

 posterior end there is but a single row owing to the proximity of 

 the myonemes. These small irregular areas contain the tricho- 

 cysts. (PI. 34, fig. 1.) 



Myonemes. — While Condylostoma is a highly contractile form, 

 it does not possess this property to the same degree that Stent or 

 or Spirosiomuni does. Engelmann ('75) has shown that the 

 entire ectoplasm of Stentor is anisotropic and therefore con- 

 tractile. In the ectoplasm of Stentor there are hyaline threads 

 which run lengthwise of the body. These have been definitely 

 correlated with the contractions of the animal and have been 

 called myonemes by Biitschli ('89). These same structures are 

 found in Condylostoma. If an individual is compressed strongly 

 under the cover glass, the contractions and expansions of these 

 fibers may be followed. 



The myoneme runs from the extreme posterior tip to the an- 

 terior end of the animal. Each fiber is continuous and does not 

 show branching as in Stentor and Spirostomum. Schuberg ( 'S6) 

 in his Avork on Stentor calls attention to the ramification zone 

 located near the posterior end of the animal, in which the myo- 

 nemes are few, but give rise to many fibers by branching. No 

 such zone can be distinguished in Condylostoma, each fiber being 

 continuous from one end to the other. The fiber begins at the 

 extreme end of the posterior tip and runs to the anterior end. 

 Other fibers are interpolated between these, but never show any 

 connection with them by means of branching as in Stentor. The 

 fibers follow the rows of cilia and give the animal a longitudi- 

 nally striped appearance. In normal individuals the myonemes 

 are closest together at the posterior end and farthest apart at the 

 middle. On the ventral surface, as the fibers proceed anteriorly 

 they separate at the posterior end of the buccal groove and con- 

 tinue to its anterior margin. None of the fibers end on the lateral 

 marsin of the buccal groove. 



