SUTTON 



2. The process of synapsis (pseudo- 

 reduction) consists in the union in 

 pairs of the homologous members 

 (i. e., those that correspond in size) of 

 the two series.^ 



3. The first post-synaptic or ma- 

 turation mitosis is equational and hence 

 results in no chromosomic differentia- 

 tion. 



4. The second post-sv^naptic divi- 

 sion is a reducing division, resulting in 

 the separation of the chromosomes 

 which have conjugated in synapsis, 

 and their relegation to different germ- 

 cells. 



5. The chromosomes retain a mor- 

 phological individuality throughout 

 the various cell-divisions. 



It is well known that in the eggs of 

 many forms the maternal and paternal 

 chromosome groups remain distinctly 

 independent of each other for a con- 

 siderable number of cleavage-mitoses, 

 and with this fact in mind the author 

 was at first inclined to conclude that 

 in the reducing divisions all the ma- 

 ternal chromosomes must pass to one 

 pole and all the paternal ones to the 

 other, and that the germ-cells are thus 

 divided into two categories which 

 might be described as maternal and 

 paternal respectively. But this concep- 

 tion, which is identical with that 

 recently brought forward by Cannon,'^ 

 was soon seen to be at variance with 

 .many well-known facts of breeding; 

 thus: 



1. If the germ-cells of hybrids are 

 of pure descent, no amount of cross- 



® The conclusion that synapsis involves a 

 union of paternal and maternal chromosomes 

 in pairs was first reached bv Montgomery in 

 1901. 



Montgomery, T. H., Jr., "A Study of the 

 Chromosomes of the Germ-Cells of Me- 

 tazoa," Trans. Amer. Phil. Soc, XX. 



■'■ Cannon, W. A., "A Cytological Basis for 

 the A-Iendelian Laws," Bull. Torrey Botanical 

 Club, 29, 1902. 



29 



breeding could accomplish more than 

 the condition of a first-cross. 



2. If any animal or plant has but two 

 categories of germ-cells, there can be 

 only four different combinations in the 

 offspring of a single pair. 



3. If either maternal or paternal 

 chromosomes are entirely excluded 

 from every ripe germ-cell, an individ- 

 ual cannot receive chromosomes (qual- 

 ities) from more than one ancestor in 

 each generation of each of the parental 

 lines of descent, e. g., could not inherit 

 chromosomes (qualities) from both 

 paternal or both maternal grandpar- 

 ents. 



Amoved by these considerations a 

 more careful study was made of the 

 whole division-process, including the 

 positions of the chromosomes in the 

 nucleus before division, the origin and 

 formation of the spindle, the relative 

 positions of the chromosomes and the 

 diverging centrosomes, and the point 

 of attachment of the spindle fibers to 

 the chromosomes. The results gave no 

 evidence in favor of parental purity 

 of the gametic chromatin as a whole. 

 On the contrary, many points were 

 discovered which strongly indicate ^ 

 that the position of the bivalent chro- 

 mosomes in the equatorial plate of the 



8 Absolute proof is impossible in a pure- 

 bred form on account of the impossibility 

 of distinguishing between maternal and pa- 

 ternal members of any synaptic pair. If, 

 however, such hybrids as those obtained by 

 Moenkhaus (Moenkhaus, W. J., "Early De- 

 velopment in Certain Hybrid Species," Re- 

 port of Second Meeting of Naturalists at 

 Chicago, Sciefice, XIII., 323), with fishes can 

 be reared to sexual maturity absolute proof 

 of this point may be expected. This observer 

 was able in the early cells of certain fish hy- 

 brids to distinguish the maternal from the 

 paternal chromosomes by differences in 

 form, and if the same can be done in the 

 maturation-divisions the question of the dis- 

 tribution of chromosomes in reduction be- 

 comes a very simple matter of observation. 



