Ch RE “TESS hd ae er ne Aw ee 
DAVIS: SPERMATOGENESIS. 1:25 
It now remains to consider the method by which the reduction 
in the number of chromosomes during synapsis is brought about. 
According to most of the older accounts a continuous spireme was 
formed during the early growth stages, which later segmented into 
the reduced number of chromosomes. Montgomery (:00) was the 
first to clearly formulate the theory that the reduction is effected by the 
union of the chromosomes in pairs, and later (:01) strongly argued that 
one of each conjugating pair is derived from either parent. ‘This 
theory of the conjugation in pairs of the maternal and paternal chro- 
mosomes during synapsis was supported by Sutton (:02, :03) and has 
now come to be generally accepted. However, there is still great 
diversity of opinion as to the manner in which the conjugation of the 
chromosomes takes place. In general two methods of chromosome 
conjugation have been described. According to one school of cytol- 
ogists the chromosomes become united end to end, while the other 
school holds that they first become arranged parallel to each other 
and then unite side by side. In both types there is, according to the 
descriptions, great variation in the details for different species of 
animals, but that need not concern us here. 
An end to end union of the chromosomes during synapsis has been 
described in amphibians by Montgomery (:03, :04), Moore and Emble- 
ton (:06); in selachians by Farmer and Moore (:05); in insects by 
Montgomery (:01, :05), Sutton (:02), Gross (:04), Farmer and Moore 
(:05), Nowlin (:06) and Stevens (:06"); in myriapods by Blackman 
(:05, :05*, :07); in Peripatus by Montgomery (:00); in Allolobo- 
phora by Foot and Strobell (:05); and in Pedicellina by Dublin (:05). 
I believe that in the Orthoptera the evidence points strongly toward 
an end to end union, but not in the manner described by Sutton (:02). 
This author described and figured the members of the autosome pairs 
as becoming united at their ends nearest the spindle pole during the 
telophase of the last spermatogonial division. I have been unable to 
find any evidence of such a fusion at this time and believe Sutton was — 
misled by an accidental approximation of the ends of the chromo- 
somes, due to their being pulled toward a common point. ‘That the 
conjugation takes place much later, is shown in Hippiscus and Melano- 
plus, where after the resting stage of the primary spermatocytes the 
chromatin collects in distinct masses, which probably represent univa- 
lent chromosomes. ‘The actual union of the chromosomes probably 
occurs at about the time these chromatin masses become converted 
into spireme threads. This agrees with Montgomery (:05), who 
describes the end to end union in Syrbula as taking place during the 
