316 University of California Publications in Zoology [Vol. 20 



In the following paragraphs a brief description of the encysted 

 forms only of Endamoeba coli will be given, since this study is con- 

 fined to the process of mitosis in that phase only of its life history. 



The cysts of Endamoeba coli vary from 10 to 25/x in diameter. 

 Larger cysts than these have been reported in the literature but they 

 may have been the cysts of Councilmama lo.flevri, and not of Enda- 

 moeba coli. 



In luistained material in fresh physiological salt solution, the 

 cysts appear homogenous, the highly refractive cyst wall standing out 

 sharply against the material of the stool. In cysts that are moribund 

 the nuclei become visible, sometimes appearing with great clearness 

 even under low powers of the microscope. In preparations stained 

 with iodine-eosin the contained structures may usually be readily 

 seen, including the nuclei, the chromatoidal bodies, and the gl.ycogen 

 mass, if the latter be present. The nuclei show the typical excentric 

 karyosome, and chromatin granules on the membrane. In permanent 

 preparations stained with iron-haematoxylin or other stains, a few 

 scattered granules may be observed on the linin reticulum which fills 

 the nuclear spaces. 



Uninucleate cysts have been exceedingly rare in the material under 

 observation, and in nearly everj^ case have presented a prophase stage 

 of mitosis (pi. 29, fig. 1). In the binucleate and quadrinucleate 

 cj'sts the majority, in the stool above referred to, showed some phase 

 of the mitotic process, but occasional individuals have been found 

 with the nuclei in the ordinary resting condition (pi. 29, fig. 2). These 

 show the typical excentric karyosome, chromatin granules on the 

 nuclear membrane, and a few scattered granules on the linin reticu- 

 lum. The greater part of the cyst in the binucleate phase is usually 

 occupied by a single, large, centrallj^ located glycogen vacuole or by 

 several smaller vacuoles, forcing the two nuclei out to the periphery. 

 The remaining space is often closely packed with acicular, splinter- 

 like, chromatoidal bodies (pi. 29, fig. 2). These vary in quantity in 

 different cysts but are almost always present in the binucleate and 

 quadrinucleate ones, sometimes in such abundance that detection of 

 the nuclei becomes an impossibility, particularly in the various mitotic 

 phases. In later stages the chromatoidal material generally becomes 

 greatly reduced in quantity, either being massed in a few large clumps 

 (pi. 31, fig. 25) or appearing as slender splinters (pi. 31, fig. 28). 

 Occasionally a few black, rounded-up granules are the only vestiges 

 of chromatoidal material remaining in the cyst (pi. 31, fig. 26). 



