96 PROTOPLASM OF PROTOZOA 



field show double refraction, as do many gels when under pressure or 

 when drawn out into threads. Mechanical stress may produce double 

 refraction in gelatin even of 0.01 percent. 



Phenomena of double refraction in protoplasm often indicate the 

 presence of mechanically and optically anisotropic elements oriented in 

 some definite way, and are among the best evidences for the presence 

 of micelles in protoplasm. See Schmidt, 1937, for a complete discussion. 



Valentin saw double refraction in the cilia of Opdina ranariim in 1861 

 and Rouget in the stalk muscle of Cctrchesium in 1862. Engelmann 

 (1875) carried out very extensive pioneering work on double refraction 

 on the Protozoa and other forms. He saw anisotropy in the pellicle 

 of large ciliates, such as Opdina, but was unable to distinguish double 

 refraction in the myonemes of Stentor because the entire outer layer is 

 doubly refractive. Mackinnon (1909) mentioned that the protoplasm of 

 Actinosphder'mm is quite generally anisotropic, and Schmidt (1937) 

 saw faint but unmistakable traces of double refraction at the edge of the 

 surface layers of Amoeba, which became distinctly greater as the amoeba 

 became rounded up before encysting, the cyst wall showing it very 

 distinctly. 



Engelmann (1875) also observed that the axopods of /I r//«cj-/'/?<im»;w 

 were doubly refractive in the living condition, the anisotropy being 

 coextensive with the axial filaments which extend deep into the proto- 

 plasm. With the withdrawal of the pseudopods the condition vanishes. 

 Mackinnon (1909) confirmed the findings of Engelmann. The structure 

 of the axial filaments of these pseudopods is known to be fibrillar (Ros- 

 kin, 1925; Rumjantzew and Suntzowa, 1925). Schultz (1915) found 

 the fibrillae in the rhizopods of the foraminiferan, Astrorhha, to be 

 doubly refractive, and Schmidt (1929) found weak anisotropy in the 

 axopods of the radiolarian, Thalasskolla. Schultz (1915) and Schmidt 

 (1929) report that the stereoplasmic axis of the pseudopods of the 

 Foraminifera are formed by the parallel alignment of fibers. 



Cilia have been found to be doubly refractive by Valentin, Engel- 

 mann (1875), and Mackinnon and Vies (1908). The latter authors 

 consider this to be caused by the depolarization of the light by reflection 

 from surfaces of the cilia, because of the difference of refractive index. 

 If air penetrates into the axis of a cilium, upon drying the anisotropy is 

 greatly increased (Schmidt, 1937). The so-called rootlets of the cilia 



