General Morphology of the Protozoa 25 



(236) indicate that coordination of the ciliary beat in Paramecium is 

 dependent upon impulses transmitted longitudinally through the ecto- 

 plasm. These findings seem to eliminate Klein's superficial network as a 

 coordinating system in Paramecium and suggest, instead, such a function 

 for the longitudinal fibrils (superficial fibrils of the neuromotor appa- 

 ratus, neuronemes of Gelei, kinetodesmas of Chatton and possibly the 

 silver-meridians of Klein). More recently, it has been concluded that the 

 cortical localization of acetycholinesterase in Tetrahymena pyriformis 

 supports the hypothesis that conduction by the fibrillar system is similar 

 to conduction along nerve fibres (201a). 



Silver-line system of flagellates 



Among the dinoflagellates, Polykrikos schwartzi (28) and such 

 gymnodinioid types as Gyrodinium pavillardi and Gymnodinium splen- 

 dens show an argentophilic surface network, while impregnation merely 

 blackens the sutures of the thecal plates in peridinioid species (6). Im- 

 pregnation of Gonium, Eudorina, and Volvox (Fig. 1. 2, D, E) demon- 

 strates silver-lines in the individual flagellates (131), while the silver-lines 

 of various Euglenida (106, 131) apparently correspond to the pellicular 

 striations visible in living material. In addition, the flagella of Pyrso- 

 nymphidae (105), as well as the pellicular ridges and the margin of the 

 undulating membrane in Trypanosoma rotatoriuyn (106), are impreg- 

 nated with silver. 



MYONEMES AND CONTRACTILE 

 STALKS 



Myonemes are well developed in various large ciliates which are 

 capable of changing form rapidly. The band-like and cross-striated 

 myonemes of Stentor coeruleus (44) extend from the posterior end of the 

 body to the adoral zone, sometimes branching to follow the rows of cilia 

 (Fig. 1. 13, A, B). Posteriorly, the myonemes turn inward and anteriorly 

 as a bundle which finally branches into fibrils that disappear in the 

 endoplasm. Among the flagellates, swimming of the medusa-like Lepto- 

 discus and Craspedotella is attributed to myonemes which bring about 

 rhythmic contractions of the body (177). Pellicular ridges in such large 

 trypanosomes as Trypanosoma rotatorium have been considered myo- 

 nemes, but their contractile nature is uncertain. Some of the larger 

 gregarines apparently possess both circular and longitudinal myonemes 

 (Fig. 1. 13, D, E) enclosed in individual ectoplasmic canals (194). Many 

 Protozoa have no myonemes but the absence of such structures does not 

 eliminate contractility. This fundamental property is exhibited by many 

 species which seem to show no appropriate differentiations at the micro- 

 scopic level. 



Well developed myonemes (stalk-muscles, or spasmonemes) are found 



