The Kansas University science bulletin, Vol. I, No. 8, September 1902
Science
The Kansas University science bulletin, Vol. I, No. 8, September 1902
Science -- Periodicals
It is first to be noted that the chromosomes lie with their longer axis
in the equatorial plate. This, as we have seen, is the plane along which
the longitudinal cleft occurred, so that a separation in this way means
the longitudinal division of the chromosomes in the first spermatocyte.
This is, in reality, what occurs. The contracting mantle fibers attached
to the middle of the segments drag the adhering chromatids apart without
at any time exposing a separating space. It is in this way that in the
beginning the longer axes are at right angles to the spindle axis and at
the end parallel with it, while during intermediate periods crosses with
arms of varying length exist (figs. 13, 14).
The previously disguised lines of separation become at once visible in
the daughter chromosomes, for, instead of remaining closely apposed, as
formerly, the chromatids spring apart at the free ends and the
chromosomes pass through the anaphase as V-shaped bodies instead of as
simple rods. The space thus disclosed represents that which separates
what would be the ancestral spermatogonial chromosomes, assuming that
the reduced number occurs by the end-to-end union of chromosomes of the
secondary spermatogonia. As already stated, the accessory chromosome
does not divide at this time.
At the end of the anaphase we find the ordinary chromosomes massed at
the poles of the cell, and, in addition, at one the undivided accessory
chromosome. The second spermatocytes are therefore of two kinds, one
possessing the accessory chromosome and the other not. One additional
feature of interest that becomes apparent during the migration of the
daughter chromosomes to the poles is the retarded division of one of the
elements (figs. 22–24). Some cysts contain cells that almost invariably
exhibit this peculiarity. The lagging chromosome is always one of the
small ones, but whether the same in each case could not be determined.
In the telophase, the main interest is centered in the question as to
whether there is a loss of identity of the chromosomes or not. The
evidence afforded by the Locustid cells is strongly in favor of the
conception of persisting elements. As is usually the case, I believe,
the chromosomes, when not under the active influence of the archoplasm,
loosen up, and their homogeneous structure gives way to the granular
appearance noticeable in the prophase. Although the chromosomes become
closely massed and granular, their outlines can usually be distinguished
(figs. 23–27). The accessory chromosome does not change its form and
structure at this time (figs. 25, 27). The telophase ends with the
ingrowth of the dividing cell-wall, and the second spermatocyte mitotic
figure is established without any real prophase. Between the two
generations it is evident that there exists no such thing as a “rest
stage.”
(_d_) _The Second Spermatocytes._
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