220 University of California PtMications in Zoology [Vol. 20 



neuromotor system or parts of it often lag behind nuclear mitosis. 

 The duplication of parabasals (pi. 26, fig. 24) proceeds most nearly at 

 the same rate with that of the nuclei, though it may be accelerated or 

 delayed, the axostyles and posterolateral flagella follow closely there- 

 after, and the other elements are less active. There is no constant 

 uniformity in the relative rates c^ the nuclei (pi. 25, fig. 22), some, 

 singly or in pairs, dividing before others. Likewise the axostyles may 

 remain undivided (pi. 26, fig. 31) while the nuclei have proceeded to 

 the 8 (at one end) -16 (at the other end) cell stage. Since the rate 

 at which cysts of Giardia die varies among cysts of the same and of 

 different stools, this variability in fission rate of different organelles is 

 an index not only of viability but of the extent of the pathological 

 conditions present among the cysts. Abnormal rates and irregularities 

 of mitotic and fission phenomena are thus indications of pathological 

 conditions in Giardia which are comparable with pathological irregu- 

 larities in cleavage and in fission in the metazoan individual. 



Nuclear conditions in the cysts throw some light on the nature of 

 mitosis in Giardia. The chromatin elongates in the axis of the nucleus 

 along the intranuclear rhizoplast (pi, 26, fig. 25), as in G. muris 

 (Boeek, 1916). Prior to the metaphase the four chromosomes assume 

 a parallel and later, in the equatorial plate, an end-to-end position 

 (pi. 26, fig. 26). There is also an increase in the amount of granular, 

 peripheral chromatin on the nuclear membrane in the prophase (pi. 23, 

 fig. 5) and a rounding up of the nucleus. The volume of the nuclei 

 decreases somewhat as the mitoses progress, but varies considerably 

 during the different phases of the process. The nuclear membrane 

 remains intact at all times. A paradesmose joining daughter nuclei is 

 sometimes seen (pi. 26, fig. 30). 



One of the most remarkable features of the encysted stage is the 

 very considerable increase in mass, 100 to 400 per cent, of the para- 

 basal bodies. In this regard they behave in close analogy with the 

 chromatoidal bodies of the amoebic cysts of the human intestine. In 

 these cysts the chromatoidal bodies develop as the glycogen mass 

 decreases and disappear after mitoses' have been completed. There is 

 no glycogen body in Giardia but the parabasals increase greatly during 

 the first two mitoses and seem to be reduced somewhat in the older 

 cysts (pi. 26, figs. 30, 31). There are occasionally small chromatoidal 

 granules (pi. 25, fig. 17) lying free in the cytoplasm, but they are 

 ephemeral and rare. They may in some instances represent remnants 

 of the peristomal fiber. 



