Life and death, heredity and evolution in unicellular organisms / by H.S. Jennings.

  • Herbert Spencer Jennings
Date:
[1920]
Catalogue details

Licence: Public Domain Mark

Credit: Life and death, heredity and evolution in unicellular organisms / by H.S. Jennings. Source: Wellcome Collection.

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    fusorian Trichomastix, found in lizards. 'Hie flagellate forms a small round cyst (Figure 41), in which the single nucleus divides into two (A), the two nuclei coming to lie one on each side of a large mass of reserve nutritive material. Then each nucleus divides twice unequally, giving off two small nuclei (Figure 41, C and D). These two small nuclei, commonly known as reduction nuclei, are absorbed and dis- appear. The remaining two nuclei, which we can now, for reasons to be clearly seen later, call half nuclei, move toward each other (E), and finally unite (F). The process of mating or of fertilization is now finished. Flere again we have a case in which the two half nuclei that unite have been developing continuously together, in a single nucleus; they separate, then (after two more divi- sions) reunite. And in this case, it is the same two nuclei that have separated that come together again,—save for the fact that each has divided off two small nuclei. The same sort of thing occurs in many lower organisms. k B Figure 43. Two methods of conjugation in Spirogyra, after Walton, 1915. A, conjugation between adjoining cells of the same filament. The contents of the cell to the right have passed into the other cell and united with its contents. B, conjugation between the cells of different filaments. From the filament above, the cell contents have passed into the cells of the filament below.
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