Note 20 — LECTURE XVIII

Emery has lately called attention to another direct proof of the existence of differential cell- and nucleus-division. According to observations made by Giardina, in the water-beetle (Dytiscus), one primitive ovum-cell gives rise, through four successive divisions, to fifteen nutritive cells and one well-defined ovum-cell. But only half of the nuclear substance takes part in these divisions, the rest remains inactive in a condensed, cloudy condition. 'The meaning of the whole process is obviously that the germ-plasm mass as a whole is handed over to the ovum-cell, while the nutritive cells receive only the nuclear constituents which belong to them' (Biol. Centralbl., May 15, 1903).