446 THE PROTOZOA 



plate." At the upper end of the body fine continuations of the longitudinal 

 myonemes can be traced to the adoral zone, ending in the basal rims of the 

 membranellae (Schroder, 867). 



Stenlor may be taken as a type showing the contractile system highly 

 developed in functional efficiency, but more or less primitive in arrangement. 

 Canals lodging the myonemes are not present universally, even in highly 

 contractile forms ; they are absent, according to Lebedew (93), in Trachelo- 

 cerca, but they are figured by Maier (73) in Prorodon teres (Fig. 186, B). In their 

 general form the myonemes are simple fibrillae, often beaded when contracted. 



In the more specialized forms the contractile system acquires a more com- 

 plicated arrangement. In Campandla, Schroder (864) describes five systems 

 of myonemes : (1) Annular myonemes of the basal part of the body; (2) longi- 

 tudinal myonemes of the outer body- wall, doubtless representing the primitive 

 system (Fig. 186, K) ; (3) annular myonemes forming the sphincter-like 

 muscle of the margin of the peristome ; (4) a spiral myoneme running under 

 the adoral spiral, and continued down the wall of the vestibule ; (5) a series 

 of retractor-myonemes of the peristomial disc. In Epistylis plicatilis, on the 

 other hand, Schroder (865) found only three systems : The longitudinal 

 myomenes (2), the annular peristomial myonemes (3), and the vestibular 

 myoneme (4). To these systems found in the Vorticellids with non-con- 

 tractile stalks must be added, in the genera Vorticdla, Carchesium, etc., the 

 powerful stalk-muscle (" spasmoneme >: ) formed by the union of the longi- 

 tudinal myonemes (Schroder, 866). In Vorticetta momlata fine connections 

 run from the hinder ciliary ring upwards and downwards to the longitudinal 

 myonemes when the cilia are developed, but disappear when these cilia dis- 

 appear. In Licnophora, according to Stevens, the fibril that runs under the 

 adoral spiral is continued down to the disc or cup of attachment and ramifies 

 in its walls. 



In the aberrant form Pycnothrip monocystoides, Schubotz describes a re- 

 markable development of the myonemes in the form of a dense plexus of 

 fibrils at the inner limit of the ectoplasm. The fibrils are connected with the 

 basal granules of the cilia, and run in two directions, forming a deeper layer 

 of circular myonemes and a more superficial layer of longitudinal myonemes. 



The question has been much discussed whether the contractile system, 

 often so highly developed, is accompanied by any conducting elements of 

 nervous nature. That many ciliates react with extreme rapidity to stimuli 

 has been noted above, and that their movements are co-ordinated is suffi- 

 ciently apparent. Neresheimer (856) describes in Stentor filaments believed 

 to be of nervous nature, neuronemes which take origin from the foot and 

 run about halfway up the body, at which point each neuroneme either ends 

 in a bulbous swelling or becomes thinner and disappears. The neuronemes 

 are situated externally to the myonemes, and run parallel to them. By 

 experiments with various drugs, Neresheimer tried to prove the existence 

 in Stentor of true nervous elements, as compared with Paramecium and other 

 forms in which neuronemes were not found, and concluded that the elements 

 described by him were truly nervous in nature. Schroder (867) casts doubt 

 on the existence of neuronemes and criticizes Neresheimer's technique. 

 Lebedew (93), however, describes fibrils, possibly nervous in nature, running 

 parallel to the myonemes in Traehelocerca. 



For the present the existence of nervous elements in Ciliata must remain 

 doubtful. But of the sensory function of the cilia there can be hardly any 

 doubt, and the fact that their basal granules are always in close proximity 

 to the myonemes is extremely significant. Such a direct contact between the 

 sensory and contractile mechanisms may render conducting elements of 

 nervous nature unnecessary, except for purposes of co-ordination of move- 

 ments. In some cilia, as already stated, the motile function is lost, and only 

 the sensory function remains. The genus Mycterothrix (Trichorhynchus) is 

 characterized by a rostrum bearing a number of stiff, tactile cilia (Faure- 

 Fremiet, 839). In some cases, however, sensory organs occur which appear 

 not to be derived from cilia, as, for example, the tentacle-like or club-shaped 



