366 Dig by. — The Cytology of Primtt la kewensis 
plasmically or chromatically ; its reaction does not depend on the fixative, 
for contrary results may be obtained in buds killed in the same manner. 
When the coming out of synapsis is completed, and the nucleus has 
returned to the centre of the cytoplasm, the beautiful looping of the continuous 
spireme is most striking (Fig. 20) ; by this time the chromatic aggregations 
have been absorbed. Although there is always a certain amount of ana- 
stamosis, it is often possible to focus the loops passing freely and separately 
within and without one another. If the spireme be both continuous and 
univalent, then the future univalent chromosomes must necessarily be 
arranged end to end in the spireme. This supposition is supported by sub- 
sequent phenomena leading to the realization of the heterotype chromo- 
somes. The loops show no longitudinal fission in their substance ; they are 
homogeneous, smooth surfaced, and faintly staining. The earliest indication 
of the association in pairs of homologous lengths of univalent spireme is the 
withdrawal of the spireme from the periphery of the nucleus, which at the 
same time becomes arranged in fewer and more distinct loops (Fig. 21). 
Uni vfc lent lengths of Spireme Joining to form the bivalent combinations 
Text-Fig. 2. 
The sides of the loops tend to approach one another and finally to join in 
places (Fig. 22). At the points of union there is always a chromatic swell- 
ing (Figs. 22 and 23). Sometimes the two sides of the same loop approxi- 
mate, sometimes it appears as if the side of one loop crossed over and 
associated itself with the side of another. The nipping in of the loops at 
the places of contact and the otherwise somewhat wide divergence of their 
sides produce a variety of figures as shown in the diagram (Text-fig. 2). 
This is the beginning of the union of univalent strands to form bivalent 
combinations. As will be shown, each side of one of these loops becomes 
eventually a univalent chromosome. By degrees the sides of the loops come 
to lie closer together, and are concentrated into more definite figures (Fig. 
24). Then each bivalent combination, the future heterotype chromosome, 
begins to dissociate itself from its fellows, and for the first time free ends are 
to be seen (Fig. 24). A still closer approximation of the univalent sides con- 
tinues, forming thick bivalent strands (Fig. 25). Sometimes this approxima- 
tion takes the form of a ladder-like union (Fig. 24), as was described in the 
loosening of the synaptic knot (Fig. 18). There is a great variety, even in 
a single nucleus (Fig. 26), in the appearance of the chromatic segments at 
