. The cell in development and inheritance. Cells. EARLY HISTORY OF THE GERM-XUCLEI 273 nection with the reduction-problem ; and some of these have raised some remarkable questions regarding the origin of reduction. A large number of observers are now agreed that during the growth- period preceding the maturation-division (p. 236),.in both sexes, the nucleus of the mother-cell (spermatogonium, oogonium), both in plants and in animals, passes through some of the changes prepara- tory to reduction at a very early period. Thus, in the egg the pri- mary chromatin-rods are often present in the very
. The cell in development and inheritance. Cells. EARLY HISTORY OF THE GERM-XUCLEI 273 nection with the reduction-problem ; and some of these have raised some remarkable questions regarding the origin of reduction. A large number of observers are now agreed that during the growth- period preceding the maturation-division (p. 236),.in both sexes, the nucleus of the mother-cell (spermatogonium, oogonium), both in plants and in animals, passes through some of the changes prepara- tory to reduction at a very early period. Thus, in the egg the pri- mary chromatin-rods are often present in the very young ovarian eggs, and from their first appearance are already split longitudinally.^ Hacker ('92, 2) made the interesting discovery that in some of the copepods {CantJiocaniptus, Cyclops) these double rods could be traced. Fig. 136. — Longitudinal section through the ovary of the copepod Canthocampttis. [H.\CKER.] og. The youngest germ-cells or oogonia (dividing at ) ; a. upper part of the growth-zone; oc. oocyte, or growing ovarian egg; ov. fully formed egg, with double chromatin-rods. back continuously to a double spireme-thread, following immediately upon the division of the last generation of oogonia, and that at no period is a true reticulum formed in the germinal vesicle (Fig. 136). In the following year Riickert ('93, 2) made a precisely similar discov- ery in the case of selachians. After division of the last generation of oogonia the daughter-chromosomes do not give rise to a reticu- lum, but split lengthwise, and persist in this condition throughout the entire growth-period of the &gg. Riickert therefore concluded that the germinal vesicle of the selachians is to be regarded as a " daughter-spireme of the oogonium (Ur-ei) grown to enormous dimensions, the chromosomes of which are doubled and arranged in 1 Hacker, Vom Rath, Riickert. in copepods; Ruckert in selachians; Born and Fick in Amphibia; HoU in the chick; Riickert in the Please note th
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectcells, bookyear1906
