956 Davis.—A Comparison of the Reduction Divisions of 
(PI. LXXI I, Fig. 60), but it is most commonly noted after'the process of 
condensation has brought the segments to a size closely approximating that 
of the chromosomes (Figs. 61-63, compare with PI. LXXI, Figs. 19-31). 
The chromosomes are not with regularity brought together in pairs during 
the second contraction, although such relations are not uncommon in 
detached groups, and in this behaviour gigas agrees with Lamarckiana and 
biennis , in contrast to the usual formation of ring-shaped bivalent chromo¬ 
somes in the writer’s material of grandiflora. 
The Heterotypic Mitosis. The prophases of the heterotypic mitosis 
in gigas give excellent stages in the development of the spindle, which is larger 
than that of Lamarckiana (compare PI. LXXI 11 , Fig. 66, with PI. LXXI, 
Fig. 27). The process of spindle formation begins, as in other Oenotheras, 
with the appearance of a web of fibrillae around the nucleus (PI. LXXIII, 
Fig. 64), the fibrillae entering the nuclear cavity with the breaking down of 
the membrane. As the fibrillae also push out into the surrounding cytoplasm 
they establish a multipolar spindle (Fig. 65), which shortly becomes bipolar 
(Fig. 66) by the rearrangement of the spindle fibres. 
The chromosomes may frequently be found end to end in chains during 
the prophases (Figs. 64 and 65), but the development of the spindle fibres 
finally brings the chromosomes to the centre of the spindle, where they 
generally lie in a crowded group until they form the equatorial plate of the 
heterotypic spindle. During the development of the spindle the chromo¬ 
somes usually take on the form of thickened V’s by bending at the ends 
and thickening in the middle regions, as in all other Oenotheras studied by 
the writer. They are similar in size to the chromosomes of Lamarckiana . 
There is no system apparent in the grouping of the chromosomes as they 
are brought to the equatorial plate. Although occasional pairs may be 
noted, the arrangement of the chromosomes is generally quite irregular 
until their alinement at the metaphase of the mitosis, when as a rule the 
two sets are clearly differentiated (Fig. 66). 
The form of the chromosomes becomes complicated as they approach 
the poles of the spindle during anaphase by the lengthwise fission which is 
so characteristic of these forms, and which is illustrated in a number of cases 
shown in Fig. 67. Thus the fourteen chromosomes that pass to each pole 
of the heterotypic spindle generally arrive and enter the daughter nuclei as 
fourteen split chromosomes (Fig. 68), although the division is sometimes 
delayed. This division, which is a premature fission of each chromosome 
in preparation for the homotypic mitosis, was, however, always shown in 
the chromosomes of the nuclei during the interkinesis (Figs. 71 and 72). 
Gates (’ 09 , p. 528) is uncertain whether the fission is always lengthwise or 
not sometimes transverse, but the writer has observed no evidence of 
departures from the manner of lengthwise division present in Lamarckiana, 
biennis i and grandiflora . 
