10 University of California Publications in Zoology [Voh. 18 



Figs. A-0. Mitosis in Giardia microti Kofoid and Christiansen. Diagram- 

 matic presentation of the nuclei figured of the individuals illustrated in plate 1. 

 X 11,000 approximately. 



Prophase figs. A-K; metaphase fig. L; anaphase figs. M-N; telophase, figs. 

 N-0. 



Fig. A. Typical resting stage of nucleus; ellipsoidal karyosome with connect- 

 ing intranuclear rhizoplast to centrosome. 



Fig. B. Mitosis begun; karyosome elongated, extension of linin to posterior 

 periphery of nucleus in the major axis. 



Fig. C. Knotlike spireme formed by contraction of chromatin at various 

 points, initiating the formation of chromosomes. 



Fig. D. Spireme band, showing longitudinal split progressing anteriorly- 

 posteriorly. 



Fig. E. Each spireme strand segmenting into four chromosomes, the action 

 progressing from the centrosome posteriorly. 



Fig. F. Eight or tetraploid number of chromosomes completely formed. 



Fig. G. Dispersal of chromosomes. Centrosome has divided, one portion 

 migrating to posterior pole of nucleus; paradesmose on outside of nuclear 

 membrane. 



Fig. H. Dispersal of chromosomes, linin connecting fibril, paradesmose 

 present. 



Fig. I. Anterior chromosomes serially homologous, or sisters, pair with each 

 other. Linin connecting fibrils and paradesmose still present. 



Fig. J. Pseudosynapsis, in a side-by-side or parasynaptic union of sister 

 chromosomes completed, forming fovir bivalent chromatinic masses. Linin sus- 

 pending the four masses and paradesmose present. 



Fig. K. Four chromatinic masses; paradesmose present; linin assuming 

 spindle-like form. 



Fig. L. Four chromatinic masses on spindle formed from linin. Chromosomes 

 dividing apparently in a transverse plane, but in what probably marks the end of 

 a longitudinal division; paradesmose no longer visible. 



Fig. M. Showing chromosomes after their division on the spindle, beginning 

 their migration to their respective poles of the nucleus. 



Fig. N. Chromosomes at each pole fused into single mass; constriction of 

 nuclear membrane. 



Fig. O. End of mitosis ; two rounded nuclei with central karyosome. Upper 

 nucleus showing rhizoplast from centrosome to blepharoplast (not figured). 



