. Cytology, with special reference to the metazoan nucleus. Cells; Cytology. 20 CYTOLOGY. coarser structure may contain larger chromatin masses which would not receive that title. No general rule can be given as to the relation of the karyosomes of the resting nucleus to the telophase or prophase chromosomes. In some cases they are portions of the chromosomes which have failed to undergo the telophase dissolution and remain as compact chromatin blocks. This is well seen in Fig. 9 {Lepidosiren). Here the anaphase chromosomes form a dense ring (daughter plate), the apices of the V-shaped chromos
. Cytology, with special reference to the metazoan nucleus. Cells; Cytology. 20 CYTOLOGY. coarser structure may contain larger chromatin masses which would not receive that title. No general rule can be given as to the relation of the karyosomes of the resting nucleus to the telophase or prophase chromosomes. In some cases they are portions of the chromosomes which have failed to undergo the telophase dissolution and remain as compact chromatin blocks. This is well seen in Fig. 9 {Lepidosiren). Here the anaphase chromosomes form a dense ring (daughter plate), the apices of the V-shaped chromosomes being on the inner circumference of the ring, while the limbs radiate outwards. At the end of telophase, when the daughter nucleus has been re- constructed, a ring of karyosomes occupies the place previously occupied by the apices of the Vs. These bodies gradually get dispersed through the nucleus and disappear, so that in the middle of the resting period they are absent. On the other hand, in many forms in which karyosomes occur they are not traceable back to the telophase chromosomes, but are secondary formations, the newly reconstructed nucleus being without them [Allium, Lundegardh, 1913). As a rule, the number of karyosomes in the nuclei of any organism is highly variable, but in other cases the number is found to be constant, and to be the same as the number of chromo- somes in the species in question, as shown by Rosenberg (1904). More- over, these karyosomes may act as centres of formation for the chromosomes in prophase, for which reason they have received the name of prochromosomes (Overton, 1906). They have been specially studied in plant cells (Fig. 10). The presence of " prochromosomes " in the resting nucleus has been taken, with some justice, as additional evidence of the continuity of the chromosomes from one mitosis to another. It must be remembered,. Please note that these images are extracted from scanned page images that may have been digitall
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectcells, bookyear1920
