4.6 Overton. — On the Organization of the Nuclei in the 
of chromosomes present in each somatic nucleus. Evidence is now in- 
creasing which seems to me to greatly favour the existence of interaction. 
This interaction could best be accomplished if the homologous chromo- 
somes are arranged in parallel pairs as Strasburger and I have described 
them, and not in different parts of the nucleus as Haecker would seem to 
have them. 
Bateson (’07) suggests that the discovery of the possibility of an 
interaction between chromosomes involving the opportunity for an inter- 
action between corpuscles representing distinct ‘ allelomorphic ’ pairs of 
characters constitutes one of the most important advances in genetics since 
the discovery of Mendel’s work. It seems to me that the arrangement 
of homologous parental chromosomes carrying more or fewer characters in 
pairs in the somatic cells of a hybrid and the consequent interaction, which 
could thus occur, would greatly aid us in explaining the puzzling com- 
plexities of heredity. 
The Conjugation of the Chromosomes in the Prophases 
of the First Division. 
All recent studies tend to show that it is during the maturation of the 
germ-cells that the parental chromosomes conjugate. The origin of the 
bivalent heterotypic chromosomes by the association of a parental and 
a maternal one as first advanced by Henking (’91) and later by Mont- 
gomery (’00, ’04), Winiwarter (’01), and Sutton (’02) has been shown to be 
general in all plants and animals studied in respect to this point, and many 
authors have agreed with Moore (’95) that synapsis is a most important 
phase in this process. 
From what he considers the strongest evidence available, Montgomery 
finds the following series of changes in the spermatogenesis of animals. 
The normal number of univalent chromosomes persists through a number 
of successive generations of spermatogonia, the last generation of which 
produce the spermatocytes of the first order. At an early period in these 
spermatocytes a pairing of homologous parental chromosomes occurs and 
the bivalent chromosomes, by a junction end to end or side by side, become 
densely grouped in synapsis during the growth period. Montgomery (’05), 
however, recently argues that the homologous chromosomes, which unite 
later in synapsis, lie next to each other during the spirem stage of the 
spermatogonia of Syrbnla. 
Recently a number of zoological investigators are inclined to believe 
that the formation of the bivalent chromosomes occurs earlier than the 
prophases of the first maturation division. Montgomery (’00, ’01) in his 
studies on Peripatus and Hemiptera maintains that the association in pairs 
occurs during the telophases of the last spermatogonial divisions, with 
which results those of Nichols (’02) on Oniscus , of Sutton (’02) on 
