. The biology of the protozoa. Protozoa; Protozoa. PHENOMENA ACCOMPANYING FERTILIZATION 313 whether or not new cirri, membranelles, and undulating membranes are formed and the old ones absorbed, has not been fully determined by observation but this appears to be the case in Uroleptus mobilis. The most important of the changes at this period have to do with the formation of the new macro- and micronuclei. The inaccurate statement is often made to the effect that the new macronucleus is formed by the metamorphosis of a micronucleus. This is strictly true only in cases of parthenogenesis. In fert
. The biology of the protozoa. Protozoa; Protozoa. PHENOMENA ACCOMPANYING FERTILIZATION 313 whether or not new cirri, membranelles, and undulating membranes are formed and the old ones absorbed, has not been fully determined by observation but this appears to be the case in Uroleptus mobilis. The most important of the changes at this period have to do with the formation of the new macro- and micronuclei. The inaccurate statement is often made to the effect that the new macronucleus is formed by the metamorphosis of a micronucleus. This is strictly true only in cases of parthenogenesis. In fertilization both macro- and micronucleus are formed from products of the amphinucleus,. Fig. 159.— Uroleptus mobilis; conjugation at the stage of nuclear fusion: g, n, gametic nuclei about to fuse; B, same enlarged; C, elongation of amphinucleus shortly after fusion. (After Calkins.) and both types of nuclei are formed by metamorphosis of such products. In the majority of cases the first metagamic division of the amphinucleus results in two equivalent nuclei. In Uroleptus mobilis this division occurs very soon after fusion and before com- plete mixture of the two pronuclei is established (Fig. 159). This is shown by the occasional finding of nuclei in which 4 of the 8 chromosomes are in the anaphase stage while the other 4 are in the metaphase (Fig. 160). The two products of this division have different fates. One of them divides again to form two nuclei which lose their vesicular character and condense into minute and. 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, Lea & Febiger
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