10 ARTHUR BOLLES LEE 
the whole length of the chromosome (with the exception of 
the extreme tips). But often, as shown in fig. 14, if seems to 
be interrupted at the polar bend, the bend only showmg an 
attenuated tract of the core without any perceptible ridge on 
it. At the tips, the spiral ceases at the base of the dome-shaped 
surface, and is not continued up to its summut, figs. 6, 7, 14. 
It seldom shows a regular pitch throughout, for its turns are 
sometimes very widely spaced, as in figs. 6 and 7, but often 
so closely approximated that they almost touch one another, 
as shown at the tip of the right-hand limb of fig. 14. The 
drawings, in which the spacmg between each turn has been 
reproduced with scrupulous care, will give a better idea of 
this than any description. 
It has been said that the spiral shows no definite limit 
inside the general surface of the axis; but outside this 
it does. Its optical section there shows as a series of minute 
conical elevations, giving, in inferior images, the appearance of 
a row of minute thorns. These elevations are figured in several 
ot the drawings of recent observers, and are by their authors 
considered to be in effect minute thorn-lke processes. But 
careful observation of well-preserved specimens (with good 
objectives and a first-class condenser) shows that the two out- 
lines of each of these apparent cones do not terminate at 
the apparent apex shown under inferior definition, but merge 
there into a single line which is continued outwards, generally 
in a perceptible curve, till it reaches the membranous sheath. 
And it can often be seen to insert on this by means of a delicate 
conical enlargement. All the drawings, figs. 2 to 18, show some 
of these lines, and the enlargement is shown very clearly in 
figs. 7 and 23, and less clearly, but still recognizably, im several 
parts of the remaiming figures. These enlargements, then, 
show as a row of minute cones having their bases applied to 
the imner surface of the sheath, and their apices contimuous 
with the line which springs from the cones on the axis. There 
is always one of these cones on the sheath for each one on the 
core. ‘Those on the sheath can often be seen to be situate, not 
diametrically opposite to those on the core, but a little higher 
