STRUCTURE OF CERTAIN CHROMOSOMES 29 
take place only at the moment of the formation of the spireme, 
or even at an advanced period of its evolution. In this case, the 
limbs pass through the interphase in a more or less widely 
divaricated state, which gives to the interphase a facies very 
dissimilar to that of the interphase of nuclei in which the 
parasyndesis has taken place at the telophase. A description 
of this is reserved for a future paper. But in either case the 
mechanism of the division of the chromosomes is the same in 
principle. There is no longitudinal splitting. 
The division is a transverse one, brought about by the 
folding of the chromosomes at their middle, and their ultimate 
segmentation at the bend there formed. The moieties which 
separate at the metaphase are the two limbs of the 
chromosome thus folded, therefore metameric, not antimeric, 
moieties 
EXPLANATION OF PLATES 1 anp 2. 
Illustrating Mr. Arthur Bolles Lee’s paper on ‘ The Structure 
of certain Chromosomes, and the Mechanism of their 
Division ’. 
Magnification 1,500 diameters throughout. 
PuateE 1. 
Fig. 1.—Anaphase of pollen grainof Paris quadrifolia. Chromo- 
somes alveolated, with sheath. 
Fig. 2.—Early interphase of pollen grain of P. quadrifolia. Chromo- 
somes without sheath, not alveolated, elongated into spirals. 
Fig.3.—Triton alpestris, Anaphase of spermatogonium. The 
chromosomes as open V’s, showing the chromatic axis and periaxial spirals 
and sheath. 
Fig. 4.—The same, a somewhat later stage, showing the chromosomes 
folded into very narrow V’s. 
Fig.5.—Bombinator igneus, spermatogonium, Portion of ana- 
phase, showing the chromosome axes and periaxial spirals, but not the 
sheath. 
Fig.6.—Salamandra maculosa. One limb of an anaphase 
chromosome, spermatogonium. Chromatic axis, periaxial spirals (very 
widely spaced), lateral processes, and sheath. 
