. Protozoo?logy. Protozoa; Protozoa, Pathogenic. FERTILIZATION BY EXOGAMY 153 1. Isogamy.—Not only may isogamous conjugation occur between full-sized and reduced-sized individuals, but among the former there may be a further difference in that the conjugating cells do not fuse to form a zygote, but separate after a few hours (copulation). This process is particularly characteristic of the infusoria and is not met with elsewhere. Fig. 60. Coiiromonas subtilis. (After Dobell.) A. normal adult cell before division, from life; B, cells in conjugation, one flagellura being withdrawn; C, fusion, fir
. Protozoo?logy. Protozoa; Protozoa, Pathogenic. FERTILIZATION BY EXOGAMY 153 1. Isogamy.—Not only may isogamous conjugation occur between full-sized and reduced-sized individuals, but among the former there may be a further difference in that the conjugating cells do not fuse to form a zygote, but separate after a few hours (copulation). This process is particularly characteristic of the infusoria and is not met with elsewhere. Fig. 60. Coiiromonas subtilis. (After Dobell.) A. normal adult cell before division, from life; B, cells in conjugation, one flagellura being withdrawn; C, fusion, first stage in "nuclear reduc- tion;" D, heteropolar division of nuclei for second "reducing division;" E, fusion of nuclei and formation of cyst; F, fertilized cell in permanent cyst. (o) The Union of Full-sized Cells.—With the exception of the lower flagellates, there are few instances of conjugation among full-sized individuals. It has been described by Schaudinn ('96) in the case of the heliozoon Adinophri/s sol (Fig. 65), where the two cells fuse after a preliminary process of maturation. Here there is little change in the normal aspect of the two conjugating cells beyond the withdrawal of the pseudopodia and secretion of a protective cyst. So, too, among some of the flagellates there is little difference in the gametes from the normal. In Bodo saltans (Dallinger) they are all alike, while in Copro- moiias subtilis, according to Dobell ('OS), one of the two cells is absorbed in the other, and its flagellum is lost, while the flagellum of the other. 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. New York and Philadelphia, Lea & Febiger
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