Abstract
An improved technique for the study of meiosis is described. The principle is based on the use of Ca- and Mg- free isotonic salt solution buffered with phosphates and of hypotonic medium without citrate. Thousands of meiotic randomly dispersed prophases may be observed in good conditions regarding not only the preservation and spreading of autosomic bivalents but also the mode of association between the X and Y inside the sex vesicle. In the Rat, it seems clear that inside the sex vesicle in pachytene the Y (heterochromatic) and the X (not heterochromatic) chromosomes are already associated “end to end” and that there is no chiasmatic relation between them. In diplotene, the Y chromosome has been seen associated by its non-centromeric end, the X, apparently by its short-arms end. The question to know whether this kind of association is peculiar to the Rat or may be generalized to all placental mammals is still under investigation. In the Sloth (Choloepus hoffmanni), the normal translocation of the Y on an autosome is cleary, demonstrable during meiosis as a peculiar type of association (trivalent).
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