MUNSON: SPERMATOGENESIS OF PAPILIO. 
105 
goes changes as follows: (a) the chromatin is massed at one side of 
the nucleus; ( b ) from this there develops a spireme surrounding the 
nucleus as a single wavy thread; (c) this is then drawn together again 
at one pole; and, from this, there emerges a double thread partly 
doubled again on itself — a double thread bent in the form of a horse¬ 
shoe; ( d) by elongation, this second doubling is accomplished; ( e ) this 
thread separates or segments between the chromosomes giving rise to 
seven tetrads; (/) the tetrads then divide into two, giving rise to four¬ 
teen diads. 
36. The spindle is developed at this time entirely from the nucleus; 
but that part of each spindle fiber extending from the centrosome to 
the second microsome ring is cytoplasmic. 
37. The first spindle fibers to appear are the central ones, extend- 
t 
ing directly from centrosome to centrosome. 
38. At first the chromosomes are scattered evenly throughout the 
nuclear space where the spindle is being formed. But later they are 
drawn together from all sides; and by the time the spindle is formed, 
they occupy the equator of the spindle. 
39. There are twenty-eight distinct chromosomes in the equatorial 
plate. As this is the somatic number, the preceding tetrad and diad 
formation must have some other significance than that usually ascribed 
to it. It may be a process of conjugation of chromosomes, an inter¬ 
change of ids, or a phase in the arrangement of the chromosomes for 
their final division in the metaphase of the mitotic process. 
40. The twenty-eight chromosomes split into halves, each half 
being drawn to its respective pole by a single spindle fiber. 
41. As the chromosomes are spherical, and equal in size, it is use¬ 
less to talk about longitudinal and transverse splitting. 
42. That the chromosomes are not bivalent is to be inferred from 
the fact that there are twenty-eight chromosomes, the somatic number 
in the equatorial plate of the first maturation division. 
43. The second, maturation division follows soon after the first. 
Occasionallv the centrosome has divided and asters are formed 
*/ 
before the first maturation division is completed. 
44. The spindle of the second maturation division, differs from the 
preceding in that it has: (a) mantle fibers formed apparently from 
the intermediate fibers of the preceding division and consequently 
devoid of chromosomes; and (6) a central spindle developed from 
the chromosomes, each central spindle fiber being connected with 
one chromosome. 
