Ig10] YAMANOUCHI—CHROMOSOMES IN OSMUNDA 9 
linin intervals; and still others (Gr&GOIRE 3, and others) conclude 
that the threads are composed exclusively of chromatin. 
Regarding the origin of the parallel threads, FARMER and Moore 
(2) and others believe they result from a longitudinal splitting; 
GREGOIRE (4), ALLEN (1), and others contend that the two are associ- 
ated but independent; and the interpretations of synapsis naturally 
differ according to the views held in regard to the structure and origin 
of the nuclear threads. 
In Osmunda, although the chromosomes during the resting period 
undergo changes so that their form differs from that seen during 
division, tracing the progressive changes makes it seem probable 
that the vacuolation does not destroy the individuality of the chromo- 
somes. On the contrary, the individual chromosomes are preserved 
as vacuolate and alveolate masses during the resting period, and 
they again reappear—in compact form at the next division. The 
interval between the heterotypic and homotypic divisions is much 
Shorter than the period occupied by their divisions, and the V-shaped 
chromosomes reappear in the exact V-form in which they entered 
into the formation of the network. 
These somatic chromosomes are of maternal and paternal origin, 
and they have come to be included within a common nuclear wall at 
the time of fertilization. After fertilization, during the succeeding 
mitoses, the individuality of chromosomes is thus maintained, and 
there is no time when these maternal and paternal chromosomes come 
into contact as regularly formed chromatin threads until the time 
of synapsis. How much difference there exists between the asso- 
Ciation of maternal and paternal chromatin material in the vacuolate 
and alveolate condition and in the form of regularly ordered chro- 
matin threads cannot be suggested; but the importance of synapsis 
as occurring only once in the cycle of chromosome history, directly 
preceding the reduction division, cannot be overestimated. 
ORIGIN OF HETEROTYPIC CHROMOSOMES 
The heterotypic chromosomes in Osmunda arise as independent 
pairs at the early prophase of the reduction division. This result 
is in accord with the views held by GrécorrE (4), ALLEN (1), ROSEN- 
BERG (12), OveRToN (11), and others. However, the method of 
