. The cell in development and inheritance. Cells. ORIGIN OF THE TETRADS 249 in copepods by Rtickert, Hacker, and Vom Rath, in pteridophytes by Calkins and Osterhout, in the onion, Allinin, by Ishikawa, and in various other forms where their history has been less clearly made out. The genesis of the ring was first determined by Vom Rath in the mole zx\c\{GrylIotalpa, '92), and has been thoroughly elucidated by the later work of Riickert ('94), Hacker ('95, i), and Paulmier ('99). All these observers have reached the same conclusion; namely, that the ring arises by the longitudinal splitting
. The cell in development and inheritance. Cells. ORIGIN OF THE TETRADS 249 in copepods by Rtickert, Hacker, and Vom Rath, in pteridophytes by Calkins and Osterhout, in the onion, Allinin, by Ishikawa, and in various other forms where their history has been less clearly made out. The genesis of the ring was first determined by Vom Rath in the mole zx\c\{GrylIotalpa, '92), and has been thoroughly elucidated by the later work of Riickert ('94), Hacker ('95, i), and Paulmier ('99). All these observers have reached the same conclusion; namely, that the ring arises by the longitudinal splitting of a primary chromatin-rod, the two halves remaining united by their ends, and opening out to form a ring. The ring-formation is, in fact, a form of. D E F Fig. 122. — Origin of tlie tetrads by ring-formation in the spermatogenesis of the mole-cricket Gryllotalpa. [\'OM RATH.] A. Primary spermatocyte, containing six double rods, each of which represents two chromo- somes united end to end and longitudinally split except at the free ends. B. C. Opening out of the double rods to form rings. D. Concentration of the rings. E. The rings broken up into tetrads. F. First division-figure established. heterotypical mitosis (p. 86). The breaking of the ring into four parts involves, first, the separation of these two halves (corresponding with the original longitudinal split), and second, the transverse division of each half, the latter being the reducing division of Weismann. The number of primary rods, from which the rings arise, is one-half the somatic number. Hence each of them is conceived by Vom Rath, Hacker, and Riickert as bivalent or double ; as representing two chromosomes united end to end. This appears with the greatest clearness in the spermatogenesis of Gryllotalpa (Fig. 122). Here. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfe
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectcells, bookyear1906
