. The cell in development and inheritance. Cells; Cells. GROWTH AND DIFFERENTIATION OF THE GERM-CELLS 125 Fol was in error in referring it to the tip. Field's conclusion is there- fore almost certainly erroneous, and he has probably confounded the centrosome with the " Nebenkern " or paranucleus. Diametrically opposed, moreover, to the results of Platner and Field are those of Hermann ('89) and Calkins ('95, 2) on amphibia and earthworms, and both these observers have devoted especial attention to the origin of the middle-piece. The evidence brought forward by the last- named author,
. The cell in development and inheritance. Cells; Cells. GROWTH AND DIFFERENTIATION OF THE GERM-CELLS 125 Fol was in error in referring it to the tip. Field's conclusion is there- fore almost certainly erroneous, and he has probably confounded the centrosome with the " Nebenkern " or paranucleus. Diametrically opposed, moreover, to the results of Platner and Field are those of Hermann ('89) and Calkins ('95, 2) on amphibia and earthworms, and both these observers have devoted especial attention to the origin of the middle-piece. The evidence brought forward by the last- named author, whose preparations I have critically examined, seems perfectly con- clusive that the at- traction-sphere or centrosome passes into the middle-piece. The "Nebenkern," which is rarely pres- ent, appears in this case to take no part in the formation of the flagellum, but degenerates without further change. In the salamander the origin of the middle- piece has been care- fully studied by Flemming and Her- mann. The latter ('89) has traced- the middle-piece back to an "accessory body" (Nebenkorper), which he believes to be not a " Nebenkern" (derived from the spindle-fibres), but an attraction-sphere derived from the aster of the preceding division, as in Lumbriciis. This body differs greatly from an ordinary attraction-sphere, consisting of the following three parts lying side by side in the cytoplasm (Fig. 63). These are : {a) a colourless sphere, {b') a minute rounded body which stains red with saffranin like the nucleoli or plasmo-. Fig. 63. — Formation of the spermatozoon from the sper- matid in the salamander. [HERMANN.] A. Young spermatid showing the nucleus above, and below the colorless sphere, the ring, and the chromatic sphere. B. Later stage, showing the chromatic sphere and ring at the base of the nucleus. C, D, E, F. Later stages, showing the transformation of the chromatic sphere into the middle-piece Please note that these images
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectcells, bookyear1896
