Archive image from page 170 of Cytology, with special reference to. Cytology, with special reference to the metazoan nucleus cytologywithspec00agar_0 Year: 1920 VI CHROMATIN AND IDIOPLASM 155 though here a complete complement of hereditary substance is bound to be present. This is probably a universal rule in oogenesis (cf. Fig. 22, etc.). Thus Gardiner (1899) calculated that in Polychaerus not more than 50 part of the chromatin of the germinal vesicle at its most chromatic stage is used up in the formation of the chromosomes of the meiotic divisions. In the sea-urchin Strongylocentrotus, Er
Archive image from page 170 of Cytology, with special reference to. Cytology, with special reference to the metazoan nucleus cytologywithspec00agar_0 Year: 1920 VI CHROMATIN AND IDIOPLASM 155 though here a complete complement of hereditary substance is bound to be present. This is probably a universal rule in oogenesis (cf. Fig. 22, etc.). Thus Gardiner (1899) calculated that in Polychaerus not more than 50 part of the chromatin of the germinal vesicle at its most chromatic stage is used up in the formation of the chromosomes of the meiotic divisions. In the sea-urchin Strongylocentrotus, Erdmann (1909) finds that the volume of the chromosomes in the pluteus is only 9V of their volume in the two-cell stage. Such considerations have led to the hypothesis of two kinds of chromatin—idiochromatin, the essential hereditary substance, or idio- plasma proper, and trophochromatin (see later under chromidia). Prob- Fig. 71. Equatorial plates of spermatogonia of three Vertebrates. A, Lepidosiren ; B, salamander ; C, rabbit. The three figures are drawn to the same scale to show the relative amounts of chromatin present in each. ably, however, the idioplasm cannot, strictly speaking, be identified with any substance. The hereditary factors should probably be considered as elementary organisms, consisting mainly indeed of chromatin but possessing an organic structure on which their activities depend. The argument therefore from equality or otherwise of mass, though weighty, is not conclusive in deciding the claims of the various constituents of the gametes to be considered as the idioplasm. There is no doubt that in animals, at any rate, a certain very small amount of cytoplasm is introduced by the male gamete along with the nucleus (see also under chondriosomes, below). This has, however, been denied in the case of some of the higher plants where it has been held that no cytoplasm enters the egg cell with the nucleus (Strasburger, 1908), but a negative is proverbially ha
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