156 Digby. — On the Archesporial and 
in pairs of chromosomes hitherto disunited, nor is it a matter of any 
importance whether the approximation occurs at a somewhat earlier or 
later period in mitosis. The really vital question at issue between the two 
schools does not, as a matter of fact, consist in Telosynapsis v. Parasynapsis 
as etymologically understood, but upon the interpretation to be placed on the 
much earlier stages of prophase in the heterotype mitosis.’ 
Telosynaptists and parasynaptists 1 are agreed as to the evolution of 
the somatic chromosomes. 2 They acknowledge the splitting into longi- 
tudinal halves (threads) of each daughter somatic chromosome during 
telophase ; the separation of the halves (threads) during interkinesis, their 
reassociation during the ensuing prophase, and their final separation as two 
daughter chromosomes during metaphase, each preparing to split again 
during telophase and thus completing the cycle. 
Those who advocate the telosynaptic theory for the origin of the 
heterotype chromosomes regard the parallel threads of the heterotype pro- 
phase as homologous with those of the somatic prophases, namely that 
each parallel thread of a pair represents half a somatic chromosome which 
separated from the other half in the preceding telophase. On the other 
hand, parasynaptists regard the parallel threads of the heterotype prophase 
as the pairing of entire somatic chromosomes. This is the fundamental and 
vital difference in the two views, and governs the interpretation of subse- 
quent stages. Telosynaptists accordingly regard the spireme that issues 
from synapsis as univalent , and claim a subsequent secondary conjunction 
of paired portions of univalent spireme, during the second contraction stages, 
to form the typical bivalent or heterotype chromosome. Parasynaptists, 
on the other hand, regard the spireme that issues from synapsis as already 
bivalent , and consequently believe that this spireme itself splits to form the 
typical univalent segments of the heterotype chromosome. Lastly, as 
a final corollary, telosynaptists hold that the paired threads, which asso- 
ciated during synapsis, separate on the homotype spindle, whereas para- 
synaptists maintain that they separate on the heterotype spindle. 
2. Modifications in the Details of Mitosis. 
It is evident that the root of the difficulty lies in the fact that as yet no 
single type has been found, whether animal or plant, which shows clearly 
and straightforwardly, with no elimination or disguising of phases, the 
whole series of events passed through during the heterotype mitosis. Each 
form has its distinctive cytological characters, and its nuclei may show one 
particular phase with exceeding clearness, whilst the pre- or post-stages 
1 These terms are employed here because they have become so widely used, and not because 
they are regarded as correct or even appropriate. 
2 It has been noted (p. 138) that a modification of the characteristic type of somatic division may 
be found (as in Primula) in which fission tends to remain closed until it splits the chromosomes 
apart on the equatorial plate. 
