. Biology; the story of living things. 162 ORGANISMS ILLUSTRATING BIOLOGICAL PRINCIPLES macronucleiis, elongates and divides twice in rapid succession. Three of the micronuclei thus formed in each cell disappear, but the fourth one divides again. In this last division two irregular masses of chro- matin are formed. This process has been likened to a similar division. inr "Xcr Conjugation in Paramecium caudafiim. Shortly after the conjugating pair come together with their ventral surfaces opposed (I) a protoplasmic bridge is formed, the macronucleus breaks down (II) and each micronudeus di
. Biology; the story of living things. 162 ORGANISMS ILLUSTRATING BIOLOGICAL PRINCIPLES macronucleiis, elongates and divides twice in rapid succession. Three of the micronuclei thus formed in each cell disappear, but the fourth one divides again. In this last division two irregular masses of chro- matin are formed. This process has been likened to a similar division. inr "Xcr Conjugation in Paramecium caudafiim. Shortly after the conjugating pair come together with their ventral surfaces opposed (I) a protoplasmic bridge is formed, the macronucleus breaks down (II) and each micronudeus divides a second time (III). What happens to three of the four micronuclei? Compare this stage with the figure on page 429 (maturation). Next the micronuclei remaining in the cell divide into two, the smaller (migratory) micronucleus passing over by the protoplasmic bridge into the opposite cell, there to unite with the larger (stationary) nucleus (VI). Trace the subsequent divisions of the fused micronucleus (VII, IX). How do we get back to the original cell condition? (X-XIV). (After Hegner.) that takes place in the eggs of animals, at the period known as matu- ration, when the sex cells are losing part of their chromatic material in preparation for fertilization of the egg by the sperm cell. The smaller mass is thought to correspond to a sperm cell of the many- celled animals, while the larger one corresponds to the egg cell. In any event, each of the smaller micronuclei migrates reciprocally over. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Hunter, George W. (George William), 1873-1948; Walter, Herbert Eugene, b. 1867; Hunter, George W. (George William), 1902-. New York, Cincinnati [etc. ] American book company
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