DAVIS: SPERMATOGENESIS. 125 



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 s\aiapsis 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 t^^^es 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), INIoore 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- 

 ])hora 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 ])ulled 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 ]\Iontgomery (:05), who 

 describes the end to end union in Syrbula as taking place during the 



