Quarterly Journal of Microscopical Science, Vol s3-96, 449-481, Copyright © 1955 by Company of Biologists

The Cell-theory: a Restatement, History, and Critique

Part V. The Multiplication of Nuclei

¹ Cytological Laboratory, Dept.of Zoology, University Museum, Oxford

I. The belief that nuclei arose by exogeny, without relation to pre-existent nuclei, was due mostly to Schleiden (1838). Kölliker (1843) supposed that new nuclei arose by endogeny within pre-existent nuclei.

2. Other early theories of the origin of nuclei contained a considerable element of truth. Many early workers thought that the ordinary nuclei of many-celled plants and animals multiplied by division (Bagge, 1841; Nägeli, 1844; von Baer, 1846), or by the disappearance of the old nucleus and its immediate replacement by two new ones (Nägeli, 1841; Reichert, 1846).

3. The history of the discovery of mitosis falls into three parts.

In the first (1842-70), chromosomes were seen accidentally from time to time, but no special attention was paid to them (? Nägeli, 1842; Reichert, 1847).

In the second (1871-8), metaphases and anaphases were repeatedly seen, placed in their right sequence, and recognized as normal stages in nuclear multiplication (Russow, 1872; Schneider, 1873; Bütschli, 1875; Strasburger, 1875.

In the third (1878 onwards), the main features of prophase and telophase were described and it was shown that the chromosomes replicated themselves by longitudinal division (Flemming, 1878-82). The separateness of the chromosomes in prophase and the constancy of their number were discovered (Rabl, 1885).

4. These researches proved that in ordinary mitosis the nucleus neither disappears completely nor divides. In certain Protozoa, mitotic division of the nucleus is a reality.

5. The indirect origin of cells, through the intermediacy of syncytia, was established by the work of Nägeli (1844), Rathke (1844, Kölliker (1844), and Leuckart (1858).

6. There is nearly always a cellular phase at some stage or other of the life-history of organisms, even when all the somatic tissues are syncytial. Certain Zygomycetes provide an exception.