1920] Kofoid—Swczy: MorpJwlogy and Mitosis of Chilomastix 131 



masses of deeply staining substance, taking, in iron haematosylin, the 

 same stain as the chromatin within the nucleus (pi. 16, fig. 11). These 

 bodies are from 0.25 to 0.9/x in greatest diameter, homogenous in struc- 

 ture, and lie near the borders of the cytostome and nucleus. In these 

 particulars they resemble the chromatoidal structures found near 

 the parabasal in the cytoplasm of Trichomonas and called by us 

 (1915) "chromidia." Their variability corresponds to that of the 

 chromatoidal rods of the cysts of Endmnoeha, with which they are 

 associated in the faeces, and suggests that they are of the same nature, 

 and meet similar needs of the organism during encystment. They 

 contain reserve materials of unknown, but probably nuclear origin, 

 contingent upon encystment. 



The organelles of the flagellate are retained to an unusual degree 

 in the encysted stage (fig. B). The nucleus {nitc.) is spherical, or 

 spheroidal with its longer axis parallel to the major axis of the cyst. 

 It is generally located a little in front of the middle of the body 

 and to the right side of the cytostome, considerably posterior to its 

 customary position in the free stage. It is 2 to 2.5ju, in diameter. 

 Its membrane maj' be very delicate with one, or several scattered 

 chromatin plaques, or it may be rather heavily encrusted with chro- 

 matin in addition to one or two large plaques which appear to bear 

 a fairly constant relation to the rhizoplast and axis of the body. 

 These two plaques are usually unequal in size, the larger often anterior 

 and at the junction of the rhizoplast with the nucleus, and the smaller 

 one at or near the opposite pole. These relations are not constant, 

 however, the j^osterior mass being the larger in some instances (pi. 16, 

 fig. 8), while in others there is only a single anterior plaque (pi. 16, 

 fig. 10). There is in most nuclei a central karyosome, less well-defined 

 than in the free stage, and often somewhat excentric in location. From 

 it there pass peripherally fine threads to the chromatin plaques or 

 other smaller chromatin aggregates on the nuclear membrane. A 

 clear, fluid-filled zone lies between the central karyosome and the 

 peripheral chromatin. 



The structure of the nucleus is suggestive of a pemianently polar- 

 ized organization not unlike that found in G-iardia by Kofoid and 

 Christiansen (1915) and by Boeck (1917). This polarization is fur- 

 ther emphasized by the presence of a small granule on the anterior 

 end of the nucleus into which the rhizoplast passes. "We interpret this 

 granule as the centrosome {cent., fig. B), since its location and mor- 

 phological relations to the nucleus, rhizoplast, and blepharoplast are 



