CHROMOSOMES OF PERLA 519 
the double threads, an actual longitudinal splitting of such 
threads cannot account for the production of the double spireme. 
According to the view of parasynaptists, the ‘pachystreptotene’ 
is the stage when each spireme segment becomes open along the 
line of synapsis. Modern telosynaptists believe that each seg- 
ment with two chromosomes conjugated end to end up to this 
stage bends at the synaptic point, and finally the constituent 
chromosomes come to lie side by side. The space enclosed by 
a ring at this stage should result from a longitudinal opening 
up of a spireme segment, if parasynaptists are correct in their 
interpretation, or, if we take the telosynaptists’ view, this should 
be the consequence of the bending of the spireme segement, two 
arms of which coming in contact with each other to form a ring. 
The process taking place in Perla is in accordance with the second 
view, as it is described in the last section. 
It must be noted, however, that the conclusion that chromo- 
somes conjugate telosynaptically can be only indirectly supported 
in the light of later history of the haploid spireme segments. 
The actual process of end to end conjugation of chromosomes 
has not been observed, and telosynapsis, therefore, shall still 
remain as an hypothesis. 
CONCLUDING REMARKS 
I have come to agree with the view of the telosynaptists in 
the case of Perla immarginata, reaching the conclusions that: 
1. Homologous chromosomes are connected to each other 
telosynaptically in the spireme. 
2. That later they bend toward each other at the synaptic 
point and become reunited parasynaptically before the meta- 
phase, thus forming rings and tetrads. 
If there be no error in my observation, and should my inter- 
pretation prove to be correct, the feeling is irresistible that at 
least some of the recent parasynaptists are misinterpreting the 
relation of the so-called ‘primary’ and ‘secondary’ splits in the 
tetrads and the nature of the split in the early spireme. It 
seems also possible that some of the very convincing figures of 
early prophase stages, those of Wenrich (717, p. 517, figs. 1 to 4), 
for instance, may be found to be partially incorrect. 
