George Lefevre and Caroline McGill 475 
ends of two chromosomes which have previously undergone a parallel 
conjugation and subsequently opened out to form a loop or ribbon. 
During the bouquet-stage, the chromosome-nucleolus, which we may 
speak of as the heterotropic chromosome, as it directly passes into this 
body without ever assuming a thread-like form, is always present and is 
frequently constricted in the middle or even completely divided into 
halves. (Fig. 2, H). 
It is not until after the bouquet-stage is passed and the chromosomes, 
in the form of bivalent threads of varying length, have scattered through 
the nucleus, that the longitudinal split becomes visible, while the inter- 
ruption at the middle of each thread becomes very conspicuous (Fig. 2, 
H and I). Delicate strands of linin may be seen bridging across the 
transverse split and connecting the halves with each other. One of the 
double ribbons is always much longer than the rest and can be traced 
continuously back to the long chromosome of the bouquet-stage and for-. 
ward to the largest tetrad. 
The heterotropic chromosome is still seen to be double, although it has 
lost its dumb-bell form and is now spherical with a distinct line of cleay- 
age dividing it into halves, as if the two rounded portions of the dumb- 
bell had flattened down upon each other (H and /). 
Late in the growth period and preparatory to the first maturation di- 
vision, the longitudinally split threads showing their quadripartite char- 
acter, as seen in the last figure, begin the process of condensation. ‘The 
longitudinal halves fuse completely and become much shorter and thicker, 
although the transverse interruption is still present as a clearly marked 
constriction at the middle point of the chromosomes. This stage is 
drawn in Fig. 2, J, in which the large bivalent is quite easily recognized. 
The odd chromosome can be followed continuously from the earliest 
stages of the growth-period, until it appears as shown at h in this 
figure. The two hemispheres have become rounded out and slightly 
drawn apart, although not completely separated, and in this condition it 
is taken up on the spindle which is formed a little later. 
The thick bivalent rods next undergo a still further condensation and 
are converted into crosses by outgrowth of transverse arms at the level of 
the constriction. These arms, however, do not extend so far as to confuse 
the original longitudinal axis, a condition which is especially conspicuous 
in the largest cross where the transverse and longtudinal arms remain 
quite unequal, although it is more or less pronounced in all. As this 
inequality in the length of the arms is retained until the crosses are taken 
up on the spindle, an identification of the long axis of the cross with that 
40 
