242 
Allen . — Nuclear Division in the 
during synapsis occurrences which seem to him to throw much light upon 
the real nature of the heterotypic division. In the synapsis stage in 
Galtonia and Thalictrum he finds (as is reported also by J. B. Overton, 
’04) that the chromatin becomes separated from the linin fibres, and, in 
the form of fine granules, aggregates into groups whose number corresponds 
to the reduced number of chromosomes which are later to be formed. The 
granules of each group unite into a small, dense body (zygosome), which 
elongates somewhat, becomes constricted in the middle, and then breaks 
up again into granules ; these become distributed along the linin, so 
forming a continuous spirem thread, which, after the disappearance of 
the synaptic condition, splits longitudinally. Strasburger considers that 
the formation of the zygosomes is a means for bringing into intimate 
contact the chromatin from two hitherto separate homologous chromo- 
somes, one paternal and one maternal ; and that the material of each 
zygosome becomes distributed along the linin thread to form a heterotypic 
chromosome, whose later transverse division has been foreshadowed in 
the constriction of the zygosome. 
The evidence for these most recently developed views is not yet 
published except in preliminary form, and it seems very difficult to bring 
them into harmony with the best-known facts as to the heterotypic figures 
in the lily. My own preparations certainly show that two longitudinal 
splittings occur during the heterotypic division. The real significance 
of these two fissions, however, can be determined only in connexion with 
the fact that early in the prophases two spirems are formed, which come 
to lie alongside of each other, and finally fuse into a single thread. Hacker 
(’02) has been able to show that in Diaptomus the double nature of the 
nucleus may show itself even as late as the prophases of the last pre- 
heterotypic division, by the formation of a double spirem. The conclusion 
is inevitable, though, so far as my observations go, not susceptible of direct 
proof, that the two spirems which fuse in synapsis contain the substances 
derived respectively from the male and female parents. It is not surprising 
that the approximation of the two spirems should result in a massing 
of their substance in a space much less than that which it formerly 
occupied. The peculiar appearances of synapsis, so far as these concern 
the material of the spirem thread, thus receive a natural explanation ; but 
the metamorphoses undergone by the nucleolar substance are not so easily 
accounted for. From my own observations, any transfer of substance from 
the nucleoles to the spirem or vice versa, at this or any other stage, seems 
to be excluded. But the constant occurrence in so many species of ex- 
tremely flattened nucleoles at the time of synapsis may perhaps have 
a significance of which as yet we can form no conception. In this con- 
nexion some observations of Hacker (’02) are of interest. One of the 
most frequent indications of the ‘ autonomy of the nuclear halves ’ is the 
