NUCLEI AND KINETIC ELEMENTS 



107 



or various species of Stcntor. The myonemes of Sfentor coernJeus 

 or Prorodon teres lie in characteristic canals, which appear hyahne 

 in contrast with the granular adjacent "ribs" of the ectoplasm. 

 Their finer structure has been made out in only a few t^pes, in 

 Stentor coeridens perhaps better than in any other. Here Schroder 

 describes a typical cross-striping due to alternate rows of light and 

 dark substance (Fig. 54 d.) 



In the majority of cases the contractile effect of the activity of 

 myonemes is possible only by their intimate connection with the 



N E. 



My 



Fig. b&.—Climacostormim sp. To show neurophanes {NE.) and myophanes {MY). 



(Original.) 



firm membranous cortex which encloses the entire animal, a con- 

 nection which makes it possible for a coordinated contraction of the 

 whole animal at once. A. retraction of special regions of the organ- 

 ism involves the attachment of one end of the contractile element 

 to some relatively fixed structure, as muscles in vertebrates are 

 attached to the endoskeleton (Fig. 55). In many cases the general 

 cortex serves this purpose as in the sphincter-like myonemes of the 

 Vorticellidse (Schroder), or the retractile elements of the "seizing 

 organ" or "tongue" of Didinium nasutvm (Fig. 89, p. ISO), or the 

 closing apparatus of the operculum-bearing types of ciliates. In 



