I. On dimensions of chromosomes considered in relation to phylogeny

Abstract

Cytologists are very generally agreed that a correspondence, more or less definite, exists between the size of the nucleus and that of the cell in which it is present. Strasburger, Gerassimow, Hertwig, Nemec and others have laid special stress on this relation, and it has been used as the basis for speculation and experiment on the inter-relation of the cytoplasm and nucleus. Strasburger, in 1893, as the result of a number of careful estimations, concluded that in young and active cells the ratio of the volumes nucleus/cell commonly approximates to 2/3. But obviously this relation can no longer hold good when the cell has so far increased in size that large sap vacuoles have come to occupy a considerable part of its total volume. Hertwig gave additional precision to the idea in formulating his well-known Kern-plasma relation. He selected as his two units the volume of the nucleus and that of the cytoplasm, instead of the nucleus and total cell dimension. A considerable amount of experimental work has shown that Hertwig’s view accords fairly closely with the results of observation and experiment and the researches of Nemec in particular are valuable in this connection. This investigator showed that by the use of chloral hydrate the cell wall normally formed between two dividing nuclei could be prevented from forming, and that failure to isolate the two cells by the partition wall was sometimes followed by a refusion of the nuclei to form a specially large one. The progeny of such a cell continued to manifest the qualities of gigantism, and the large nuclei, and correspondingly large cells, could easily be recognised in the tissues which had undergone the chloral hydrate treatment indicated above. Observations made by Miss H. Kemp in London only served to confirm Nemec’s statements on this point.