Structural Differentiation of the Nucleus 121 



changes in direction of the major coil or in the sahvary gland 

 chromosomes, explained them away, or in some cases ignored them, 

 because they could not, of course, be accommodated to a theory 

 having this basis. Similarly, many other workers presented figures 

 of drawn-out major spirals as evidence for the minor spiral concept 

 of Fujii, Kuwada, et al. Further confusion resulted from disagree- 

 ment on the number of chromonemata within meiotic chromosomes. 

 Kuwada and Nakamura (1933) , in one of the first presentations in 

 English of the work of the current Japanese school, showed the coil- 

 within-a-coil structure by means of a diagram containing four 

 strands. This diagram was adopted by the Darlington school since it 

 agrees with their concept of the number of strands. Kuwada and 

 Nakamura had, however, already pointed out in publications in 

 Japanese that there is a further split in each of the chromatids in 

 the second division, and they stressed this point in a publication in 

 English in the following year (1934) . They and others have since 

 brought forward much evidence for the existence of at least eight 

 strands in a meiotic bivalent. The Darlington school, however, still 

 sees only four. It is obvious that optical images can be given very 

 different interpretations as coils when such a disagreement exists 

 on the number of strands. It has also been pointed out (Huskins, 

 1937) that the minor coil of some workers is a tightly wound helix, 

 while that of others is a mere waviness. The former would most 

 easily be explicable as the result of its molecular structure; the 

 latter may be interpreted as the initiation of a spiral determined 

 by mechanical forces. There are also differences of opinion on the 

 relationship between the two major coils formed by the two chroma- 

 tids of a meiotic chromosome. Some authors have pictured them as 

 intertwined; to get them separated Matsuura has postulated breaking 

 and rejoining (genetic crossing-over) during anaphase — for which 

 there is no evidence. Most observers, however, find the chromatid 

 spirals twisted on their own axis but free of each other. 



In the hope of resolving these differences of opinion on the 

 interpretation of microscopic images, efforts have been made, but 

 with very meager success, to obtain evidence from other levels. 

 Polarized light experiments were for some time held to prove the 

 existence of a minor spiral at right angles to the major spiral, but it 

 is now generally conceded that the existing data on birefringence 

 of chromosomes are equivocal (cf. Frey-Wyssling, 1938) . Innumer- 

 able experiments have been made to determine the number of 

 chromonemata through the breakage effects of X-rays. The results 



