. The biology of the Protozoa. Protozoa; Protozoa. 368 BIOLOGY OF THE PROTOZOA Macronuclei are generally regarded as ''somatic" nuclei with an important part to play in general metabolism. They disappear by absorption and are replaced by products of micronuclear division at periods of reorganization by "endomixis," or by products of amphi- niiclei after conjugation. Chromosome formation, with a definite number of chromosomes, has been made ovit for a number of species of ciliates, but no definite chromosomes have been described from macronuclei. Evidence is accumulating to indic
. The biology of the Protozoa. Protozoa; Protozoa. 368 BIOLOGY OF THE PROTOZOA Macronuclei are generally regarded as ''somatic" nuclei with an important part to play in general metabolism. They disappear by absorption and are replaced by products of micronuclear division at periods of reorganization by "endomixis," or by products of amphi- niiclei after conjugation. Chromosome formation, with a definite number of chromosomes, has been made ovit for a number of species of ciliates, but no definite chromosomes have been described from macronuclei. Evidence is accumulating to indicate that the micro- nucleus is the essential element of the cell in conjugation but other evidence is at hand to show that it is not essential for continued. J // * A O J ^ i i ' "-^ n '-i r^ Ft t'M>// "^^ ^^^s^ ^i-^ â¢\;~^.^Z^j<. "^H^ â a^ Fig. 159.âDendrosoma elegans; n, nucleus. (From Calkins after Kent.) vegetative life or for reproduction by cell division. Thus amicro- nucleate races of Paramecium, Didinium, Spathidiu7)i, Oxytricha, etc., have been maintained for long periods by Woodruff, Dawson, and others, while Maupas, Calkins and others have shown that the micronucleus may disappear in long-continued cultures of hypo- trichous forms, although the organisms are still able to divide (p. 72). It is evident that different macronuclei represent difl'erent degrees of specialization and that some forms may carry on all processes of asexual activity without a micronucleus and represent transition stages to the opalinids in which there is no nuclear. 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 Calkins, Gary N. (Gary Nathan), b. 1869. Philadelphia, New York, Lea & Febiger
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