. The cell in development and inheritance. Cells. 254 REDUCTION OF IJII: CHROMOSOMES In the first of his classical cell-studies Ikneri (^^7, i) reached the same result through a careful study of Ascaris nicgalocephala, showing that each tetrad aj^pears in the germinal vesicle in the form of four parallel rods, each consisting of a row of chromatin-granules (Fig. 117, A-C\ He believed these rods to arise by the double longitudinal splitting of a single primary chromatin-rod, each cleavage being a. Fig. 126. — Tetrad-formation in an insect, Anasa. [Paulmier.] A. Resting spermatogonium with singl
. The cell in development and inheritance. Cells. 254 REDUCTION OF IJII: CHROMOSOMES In the first of his classical cell-studies Ikneri (^^7, i) reached the same result through a careful study of Ascaris nicgalocephala, showing that each tetrad aj^pears in the germinal vesicle in the form of four parallel rods, each consisting of a row of chromatin-granules (Fig. 117, A-C\ He believed these rods to arise by the double longitudinal splitting of a single primary chromatin-rod, each cleavage being a. Fig. 126. — Tetrad-formation in an insect, Anasa. [Paulmier.] A. Resting spermatogonium with single plasmosome and two chromatin-nucleoli. B. Equa- torial plate of dividing spermatogonium; twenty large and two small chromosomes. C. Final spermatogonium-division. D~I. Prophases of first maturation-division. D. E. Synapsis, with single chromatin-nucleolus. F. Segmented split spireme. G. H. Formation of the tetrad-rings. H. I. Concentration of the rings to form tetrads. preparation for one of the polar bodies. In his opinion, therefore, the formation of the polar bodies differs from ordinary mitosis only in the fact that the chromosomes split very early, and not once, but twice, in preparation for two rapidly succeeding divisions without an intervening resting period. He supported this view by further obser- vations in 1890 on the polar bodies of Sagitta and several gastero- pods, in which he again determined, as he believed, that the tetrads. 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 perfectly resemble the original Wilson, Edmund B. (Edmund Beecher), 1856-1939. New York Macmillan
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