386 
M. G. Sykes 
they believe to represeut a bivalent chromosome of wbicb tbe 
univalent members diverge from one anotber; in Funkia however, 
the fission in tbe spireme can often be seen extending round tbe 
loops and it will be shown that the Separation which occurs in the 
heterotype takes place along the line of this fission. 
V. Formation of chromosomes. Figs. 39— 40, PI. IX show 
the next stage in which the spireme is divided up into double Seg- 
ments which are still unevenly scattered throughout the nuclear ca- 
vity. This stage is of very common occurrence in my preparations, 
a fact which appears to indicate that after Segmentation is complete 
some little time elapses before auy further change takes place. 
The Segments are sometimes straight, more often curved but 
generally in the form of loops: irregulär fibrils of linin can again 
be seen projecting from the chromomeres 1 ). Fine tlireads of linin 2 ) 
also connect the ends of the Segments (Fig. 38. PL IX.); the existence 
of these structures seems to suggest that the Segments are not formed 
by the abrupt Segmentation of the spireme, but by a gradual Col- 
lection of material into specialised areas, which remain connected for 
a time by one, or generally two, delicate threads. The individual 
Segments are of various lengths but there is no reason to suppose 
that all are homologus with the fully formed chromosomes of a 
later stage. It is possible that some of the longer segments already 
correspond to the large chromosomes; indeed five or six much longer 
than the others can usually be found in a nucleus. In some cases, 
such as in Fig. 43. PI. IX, a break at the bend of what appears to 
have been a large loop suggests that here two large pairs of chro- 
mosomes are arising from one original Segment. The shorter chro- 
mosomes are still united together in rows of three or more (Figs. 41, 
42, 43, 44. PI. IX.). Finally these rows break up and the short 
chromosomes becorne arranged round the periphery of the nucleus. 
In some well differentiated preparations the chromatin can be seen 
to be aggregated into two dense masses in each member of a pair 
of short chromosomes, producing a tetradlike appearance; this is seen 
in Fig. 45. PI. IX., the line separating the pair being that of the 
longitudinal split in the spireme. 
The six long pairs of chromosomes are usually found nearer the 
centre of the cavity and one or more of them is often in connection 
1) Cf. p. 5 & Fig. 29. PI. VIII. 
2) Miyake, 1906. Fig. 54 Taf. IV. Figs. 120, 124 Taf. V. Atkinson, 1899. 
p. 5. Figs. 3, 8, 9, 10 PI. I. 
