. Evolution and animal life; an elementary discussion of facts, processes, laws and theories relating to the life and evolution of animals . FIG. 155.—Reduction of chromosomes in the spermatogenesis of Ascaris megalocephalavar. biralens: A, Nucleus of a spermatogonium, the typical number of chromo-somes (4) shown, each split longitudinally preceding the nucleus fission; B, youngsplitting primary spermatocyte, two tetrads present, each with body double fromlongitudinal splitting of a chromatin thread; C, the tetrads in the equatorial stageof fission; D, separation of the dyads; E, the dyads in
. Evolution and animal life; an elementary discussion of facts, processes, laws and theories relating to the life and evolution of animals . FIG. 155.—Reduction of chromosomes in the spermatogenesis of Ascaris megalocephalavar. biralens: A, Nucleus of a spermatogonium, the typical number of chromo-somes (4) shown, each split longitudinally preceding the nucleus fission; B, youngsplitting primary spermatocyte, two tetrads present, each with body double fromlongitudinal splitting of a chromatin thread; C, the tetrads in the equatorial stageof fission; D, separation of the dyads; E, the dyads in succeeding fission of thesecondary spermatid; F, completion of the fission of the same, each cell (spermatid)contains the reduced number of chromosomes (2). (After Brauer.) number of the chromosomes in the first division, and isusually arranged in tetrads, or groups of four rounded,deeply staining bodies connected by linin fibers. These tetradsare always one half the number of the original rod- or thread-like chromosomes. Thus in Fig. 155, A represents a sperma-togonium nucleus of Ascaris with the four chromosomes,showing the longit
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