396 Philippine Journal of Science 19 1» 



CYTOLOGY 



The organism is clothed with a fairly thick cuticle — homog- 

 enous, transparent, and refractive. Under ordinary conditions 

 this cuticle appears to be firm enough to keep the shape of the 

 animal constant, and yet under certain circumstances it is seen 

 to be flexible enough to allow considerable movement and change 

 of shape. The cuticle is traversed by longitudinal lines or stria- 

 tions, which on the dorsal surface run from pole to pole ; on the 

 ventral surface, anteriorly, they curve dorsad and converge, 

 following the depression that marks the position of the adoral 

 zone. From these lines spring the comparatively long, slender, 

 and delicate cilia, the coordinated fibrillary movements of which 

 propel the animal forward. I have been unable to demonstrate 

 basal granules at the origin of the cilia. It is not certain that 

 these longitudinal lines actually are ridges because in cross sec- 

 tions of the organisms the cuticle does not show any raised 

 or differentiated areas. It is probable that the lines represent 

 the insertion of myonemes, the contractions of which bring 

 about the movements of the body. The seeming absence of 

 basal granules might be explained on the basis of the supposi- 

 tion that kinetic elements, common to both the myonemes and 

 the cilia, are contained within the myonemes. 



These lines are plainly visible in the living organism, but are 

 hard to distinguish in the fixed and stained specimens. While 

 the contractile mechanism of this species is somewhat similar 

 to that seen in the closely related genera Stentor and Spiros- 

 temum, the body does not show the high degree of contractility 

 exhibited by those two nonparasitic forms. 



The medulla consists of two distinct cytoplasmic zones ; namely 

 a finely granular ectoplasm, and a coarsely granular endoplasm. 



The ectoplasm consists of a narrow strip of clear, almost 

 homogenous, refractive, and finely granular cytoplasm around 

 the periphery of the cell which, just above the terminus of the 

 cytopharynx and at the level of the oral depression, apparently 

 expands and becomes continuous with an area of similar struc- 

 ture occupying the anterior third of the organism. This is 

 probably an optical effect due to the thinness of the body at 

 this point and where the endoplasm would appear to be relatively 

 scant in quantity. 



This anterior third of the animal is a blunted cone which 

 is excavated ventrally. Its base is represented by a line of 

 demarcation sharply seen (see fig. 2, b and c) , especially in the 



