CHROMOSOMES AND MITOCHONDRIA 251 
associated two by two? (2) Admitting the fact of 
synapsis, are the conjugating elements chromosomes, 
and are they individually identical with those of 
the last diploid or pre-meiotic division? (3) Do 
they conjugate side by side (parasynapsis, parasyn- 
desis), end to end (telosynapsis, metasyndesis), 
or in both ways? (4) Does synapsis lead to partial 
or complete fusion of the conjugating elements to 
form ‘zygosomes’ or ‘mixochromosomes,’ or are 
they subsequently disjoined by a ‘reduction-divi- 
sion’? Upon these questions depends our answer 
to a fifth and still more important question, namely, 
(5) Can the Mendelian segregation of unit-factors 
be explained by the phenomena of synapsis and 
reduction ?” 
The behavior of the chromosomes during synapsis 
in the germ cells of the male is indicated diagram- 
matically in Fig. 62, the terms used being those 
proposed by von Winiwarter (1901) in his work on 
the odgenesis of the rabbit. In the spermatogonia 
(Fig. 62, 1) the chromatin is arranged in clumps on 
an achromatic reticulum; in the spermatocyte 
(Fig. 62, 2) it breaks up into granules which become 
arranged in single rows or filaments (the leptotene 
threads). These leptotene threads later become 
paired (synaptene stage, Fig. 62, 3) and converge 
toward the side of the nucleus near which the centro- 
some and centrosphere are situated (Fig. 62, 4), a 
condition known as synizesis. The granules of the 
leptotene filaments approach and finally fuse so 
as to produce single thick threads (Fig. 62, 5-7); 
