338 University of California. Publications in Zoology [Vol. 20 



living animals isolated in small drops, but after having been dis- 

 covered there they were found in whole mounts stained with both 

 Mallory's and iron haematoxylin. The lines of basal granules were 

 also brought out when the animals were killed in 10 per cent formalin 

 and fixed twenty -four hours in the dark in Von Rath's osmic acid 

 picro-mercurie fixative. 



When animals were killed in 1 per cent strychnine solution, the 

 cytoplasm, with the included trichocysts, contracted to a small sphere, 

 leaving the transparent pellicle in its original position. The tricho- 

 cysts were then discharged and looked like astral rays protruding 

 from the cytoplasm. The clearest views of the ciliarj' lines in the 

 pellicle were then obtained. Wonderfully clear views of trichocysts 

 and basal granules were also obtained when animals killed in con- 

 centrated bromine water were placed on a slide and a little aniline 

 blue solution run under the cover. 



MORPHOLOGY 

 Brief Description of Paramaecium 



In describing Paramaecium, the terms oral and aboral will be used 

 instead of dorsal and ventral. Otherwise, the terminology is the 

 some as that used for bilaterally symmetrical animals. 



Paramaecium was well described by Ellis (1769) as "an animal 

 with a longish body and a groove in one end like a gimlet." The 

 cytostome, a slit-like aperture, extends from the caudal end of this 

 groove and lies in the posterior two-thirds of the body. It is con- 

 tinued as the cytopharynx which runs obliquely caudad to the 

 vicinity of the posterior contractile vacuole. There are two contractile 

 vacuoles, one anterior and one posterior, which pulsate rhythmically 

 about twenty times per minute. The macronucleus is oblong, deeply 

 staining about one-third as long as the body, and its posterior end 

 lies near the anterior end of the cytostome. The micronucleus com- 

 monly lies in a little groove in the macronucleus. The cytoplasm 

 contains numerous food vacuoles in continual cyclosis. 



Neuromotor Apparatus 



In this work, studies have been made of the outer endoplasm and 

 the ectoplasm and pellicle. The ectoplasmic structures include the 

 cytostome and cytopharynx, also longitudinal rows of cilia, and 

 trichocysts which we have found to be arranged in whorls. The 



