ELECTRO-PHYSIOLOGY 



CHAP. 



that these structures are transitional stages between pseudopodia 

 and muscle-fibrils proper. 



If we examine a large transparent Vorticella under the high 

 power, it is easy to detect delicate, converging fibrils just below the 

 surface ; they run parallel with the axis of the body, and are often 

 finely varicose. Here we undoubtedly have a differentiation 

 product of the ectoplasm (Fig. 1), whether with Biitschli (3) 

 we regard these fibrils merely as a longitudinal series of cells 

 within the otherwise alveolar protoplasm, or as a special structural 

 arrangement. These fibrils (myonema) converge towards the 

 junction of the stalk, there, in most cases, uniting into a cylindrical 



filament, which appears fibrillated 

 throughout in optical transverse section. 

 Certain of the Heterotricha (Stentor, 

 Spirostomum) and Holotricha (Holo- 

 phyra, Prorodon, Opaliniden) are char- 

 acterised by a much more pronounced 

 development of muscular fibrils. Those 

 of Stentor, isolated by Engelmann, 

 were as much as 1/z, in diameter. There 

 were even indications of a finer struc- 

 ture, i.e. a kind of transverse striation 

 (3, p. 1000). 



Lieberkiihn recognised the fibrils 

 of Stentor as contractile elements. He 

 observed that while invariably straight 

 in contracted Stentors, they assume 

 an undulatory appearance as soon 

 as the infusorium begins to lengthen, becoming elongated during 

 relaxation. As the animal grows longer, the waves become 

 flatter. The fibrils eventually become quite straight again, and 

 are more and more drawn out with continued extension. In the 

 foot, which is most protracted, they lose all separate identity ; in 

 the rest of the body they resemble lines of excessive fineness. 

 " If, as often happens, the animals shrink slowly together during 

 several seconds, instead of contracting suddenly, the fibrils, 

 instead of being short, thick, and straight at the maximum of 

 contraction, will be distinctly wave -like, and not perceptibly 

 thicker than in the ordinary extended state of the animal. The 

 waves are often so steep and short that the fibres come into 



FIG. 1. Carchesium polypinum. 

 (Biitschli.) 



