126 University of California Publications in Zoology [Vol.20 



tion and expansion of the cytostome give differing pictures of the 

 relations of the peristomal fiber to the underlying organs. 



The deeply stained periphery of the cytostome of Chilovwstix owes 

 its appearance to two structures whose analysis in preparations is most 

 difficult and whose morphological interpretation offers an interesting 

 problem. These organs are the parastyle and the parabasal body. 

 They so much exceed the peristomal fiber .in volume and stainability 

 that they appear largely to have been the structures interpreted as 

 the cytostome and drawn as its margin by previous investigators 

 (Brumpt, 1913; Prowazek and Werner, 1914; Kuczynski, 1914; and 

 De Fonseca, 1916), except Chalmers and Pekkola (1918). The last 

 named note the distinction between the peristomal fiber and the 

 underlying stained structures. 



The parabasal (fig. A, par. b.) is a deeply staining, curved rod 

 which runs posteriorlj^ from the tertiary blepharoplast. Its course 

 follows approximately that of the right margin of the cjiiostome but 

 posteriorly it extends beyond this opening and lies deep in the cyto- 

 pla-sm, curving to the left around the posterior end of the oral pouch, 

 extending anteriorly for a short distance on its left side, and ending 

 in a fine point near the posterior end of the parastyle. 



In some cases (pi. 16, fig. 8) it appears to adhere to the peristomal 

 fiber for a short distance, in others it is free from that fiber throughout 

 its whole length. The parabasal is imbedded in the right wall of the 

 oral poiich. In imperfectly decolorized individuals this whole wall 

 may retain the stain or the fiber be buried in the lateral sheet of 

 stained material. The curvature of the parabasal varies according 

 to the state of its contraction. When the cytostome is wide open the 

 parabasal may be exposed (pi. 16, fig. 10) inside of the cytostoraal 

 opening, and when the lips are contracted and the cytostome reduced 

 to a constricted, slipper-shaped opening (pi. 16, fig. 11), the parabasal 

 is outside of the opening on the right side of the body. It usually 

 entends posteriorly beyond the end of the cj'tostomal opening (pi. 16, 

 fig. 13) but may be included within it (pi. 17, fig. 16). These varying 

 pictures of its relations to the cytostome are records of the mobility 

 and exhibit stages of the contraction of the overlying peristomal fiber. 

 As Chalmers and Pekkola (1918) state, the inner and outer lips may 

 contract so as almost to touch each other, forming overhanging lobes 

 (pi. 16, fig. 8) in the anterior half of the opening. Such a lobe may 

 form on one side only. These movements of the cytostome are sug- 

 gestive of the food-gripping function observed by the authors cited 



