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 oogenesis 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) ; 



