72 2 CALKINS. [Vol. XV. 



When the latter are completely formed, these granules fill the 

 remainder of the nucleus, the basichromatin of the chromo- 

 somes occupying no more space apparently than when in the 

 form of Ivaryosomes. ^ 



/;. Metapliase. — At this period the chromosomes are single, 

 thick rods or fibers of chromatin and distinctly granular, 

 although each granule is much larger than one of the original 

 elements. Shortly afterwards, however, the chromosomes 

 become double, consisting then of two rows of granules 

 formed by a longitudinal cleft down the middle line (Fig. 38). 

 The main part of the chromosomes does not lie in the center 

 of the nucleus as usual in other Protozoa (Actinospliaeriiim, 

 EiiglypJia, etc.). On the contrary, the chromosomes lie in a 

 linear group with their ends close against the membrane of 

 the nucleus at the side nearest the sphere (Figs. 8, 11, 26). 

 At this stage, or even before (Figs. 12 and 14), the nucleus 

 begins to elongate in a direction which for convenience may 

 be called the "primary a.xis," the ends of the chromosomes 

 being arranged in the median line of the nucleus, that is, along 

 the primary axis (Fig. 14). The nucleus thus assumes the 

 appearance of a cylinder with rounded ends, the chromosomes 

 extending from the margin nearest the sphere towards the 

 opposite side (Fig. 14). This stage is rarely seen, however, 

 for the elongate nucleus soon bends around the central-spindle 

 to form a C-like figure (Figs. 12, 13). In many cases the 

 curvature along the primary axis and the elongation of the 

 nucleus are simultaneous and not separate actions. The curva- 

 ture continues until the extremities of the primary axis become 

 more or less closely approximated (Fig. 13). 



By the curvature of the nucleus the chromosomes are carried 

 around the central-spindle until they form an incomplete ring. 

 They become focused at the point x of the Fig. ©, which is 

 formed by the curvature of the nucleus. The axis in which the 

 central-spindle lies may be called the " secondary axis " (Fig. 



13). 



c. Anaphase. — The structure of the chromosomes in the 

 nuclear plate and their subsequent changes can be studied only 

 in sections. These may be cut either transversely or longitu- 



