Studies in Spermatogenesis, Vol. 2: Pages 33-74, Plates VIII-XV: A Comparative Study of the Heterochromosomes in Certain Species of Coleoptera, ... to Sex Determination (Classic Reprint)
In Trz'r/zabda canadense the Spermatogonial chromosomes are invaria bly smaller than in T. Vz'rgata, but similar size relations prevail. The Spermatogonial plate (fig. 21) contains 30 chromosomes, 29 large and 1 extremely small. In the growth stages the association of the two unequally paired chromosomes with a rather large plasmosome is more evident than in T. Vz'rgata (figs. 22 In this Species the unequal pair is more often found at a different level from the other chromo somes in the early metaphase of the first maturation mitosis (fig. But it later comes into the plate with the other chromosomes (figs. 2 5 and divides earlier than most of the other bivalents (fig. In a polar view of this metaphase the largest chromosome often appears double (fig. 28) in a front view it is a tetrad as in T. Oz'rgata, figure 10. Figure 29 is the equatorial plate of a metaphase in which the larger component of the unequal pair has been removed in sectioning. The daughter plates of a first Spermatocyte in anaphase (fig. 30) Show the separation of the components of the heterochromosome pair and equatorial plates of the resulting two classes of second spermato cytes (fig. 31) Show the same conditions. Figures 32 and 33 are prophases of the second division, figure 33 showing the small chromo some ready for metakinesis. It was impossible here also to get good drawings of daughter plates of the second spermatocytes to Show the content of the two classes of spermatozoa, but there is no doubt that all of the chromosomes divide in the second mitosis, giving one class of spermatids containing the small chromosome, the other class its larger homologue.
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