The cell in development and inheritance / by Edmund B. Wilson.

  • Edmund Beecher Wilson
Date:
1902, ©1900
Catalogue details

Licence: Public Domain Mark

Credit: The cell in development and inheritance / by Edmund B. Wilson. Source: Wellcome Collection.

Provider: This material has been provided by the Francis A. Countway Library of Medicine, through the Medical Heritage Library. The original may be consulted at the Francis A. Countway Library of Medicine, Harvard Medical School.

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    nucleus with no trace of a centrosome. In this same form, as described above, the ordinary vegetative mitoses are quite of the metazoan type, with a persistent extranuclear centrosome. The history of the chromatin in the mitosis of unicellular forms shows some interesting modifications. In a considerable number of forms a more or less clearly marked spireme-stage precedes the forma- tion of chromosomes (diatoms. Infusoria, dinoflagellates, Eiiglypha); in others, long chromosomes are formed without a distinct spireme- stage {Noctiluca). It has been clearly demonstrated that in some cases these chromosomes split lengthwise, as in Metazoa {Noctiluca, Fig. 43. —Mitosis in Paranmba. [SCHAUDINN.] At the left, amoeboid phase, showing nucleus and Nebenkorper. At the right, four stages of division in the swarm-spores. diatoms, Actinophrys, probably in EuglypJia); but in some cases they are stated to divide transversely in the middle (Infusoria according to Hertwig, Ccratinm according to Lauterborn). These chromosomes appear always to arise, as in Metazoa, through the linear arrangement of chromatin-granules {Noctiluca, ActinospJicerium, Etiglena), which themselves in many cases arise by the preliminary fragmentation of one or more large chromatin-masses {e.g. in A\}ctiliica or ActiiiospJicz- riiint). In other forms no such linear aggregates are formed, and direct fission of the chromatin-granules appears to take place without the formation of bodies morphologically comparable with the chromo- somes of such forms as Noctiluca. This is apparently the case in Tetrainitus, and AcJiroviatiuvi, other forms having a distributed