. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. SPERMATOGENESIS OF THE DRAGON-FLY. 279 apart are brought close together. At first the long axis of the loop coincided with the plane of union in synapsis, but with the bending of each autosome the long axis is reversed and lies at right angles to the original long axis. The ends where the chromo- somes united do not bend, but remain extended to form side arms. A cross is thus produced by ftris process, the upper half composed of one univalent autosome and the lower half of another. When the signet ring condenses it assumes t
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. SPERMATOGENESIS OF THE DRAGON-FLY. 279 apart are brought close together. At first the long axis of the loop coincided with the plane of union in synapsis, but with the bending of each autosome the long axis is reversed and lies at right angles to the original long axis. The ends where the chromo- somes united do not bend, but remain extended to form side arms. A cross is thus produced by ftris process, the upper half composed of one univalent autosome and the lower half of another. When the signet ring condenses it assumes the same form as the others; all finally become condensed crosses showing a less dense area in the middle. Figs. 39, 40, and 41 show cells containing a number of crosses, and in Figs. 40 and 41, the sex-chromosome which has retained its round compact form through all the stages of the growth period appears. In some prophases as many as nine different sizes of crosses which would form bivalent chromosomes of the primary spermatocyte could be counted. The largest bivalent autosome comes from a cross in which the secondary long axis is much extended and the united ends of the univalent auto- somes bulge only slightly to form exceedingly short side arms (Fig. 41). (c) First Spermatocyte Division. The chromosomes, as last described, have become bivalent masses; with only an area less dense in the center to indicate the former central split. As just described, each bivalent^has four projecting parts corresponding to the arms of a cross. Hence, if a bivalent is cut exactly in two, one half when viewed. from the cut surface shows two ends connected by a cross piece below the level of the ends. It is difficult to give an adequate idea by a description but the text figure makes this clear by picturing the result in cross-section of different cuts through the Please note that these images are extracted from scanned page images that may have been digitally enhanced for readabilit
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
