. Cytology, with special reference to the metazoan nucleus. Cells; Cytology. 208 CYTOLOGY massed together into a " chromidial net " which forms a ring round the edge of the cell. The Arcella therefore now consists of a cell with two nuclei (primary nuclei) and a chromidial net. At certain stages of the life history secondary nuclei are formed in large numbers out of the chromidial net, by the aggregation of chromidia into small masses. These secondary nuclei multiply by mitosis, and ultimately may give rise either to asexual buds or to gametes. An unusual type of syngamy is sometimes
. Cytology, with special reference to the metazoan nucleus. Cells; Cytology. 208 CYTOLOGY massed together into a " chromidial net " which forms a ring round the edge of the cell. The Arcella therefore now consists of a cell with two nuclei (primary nuclei) and a chromidial net. At certain stages of the life history secondary nuclei are formed in large numbers out of the chromidial net, by the aggregation of chromidia into small masses. These secondary nuclei multiply by mitosis, and ultimately may give rise either to asexual buds or to gametes. An unusual type of syngamy is sometimes observed in this animal, involving fusion or mingling of chromidia (chromidiogamy, Swarczewsky) rather than of formed nuclei. Two Arcellas, in which the primary nuclei have degenerated and all the chromatin is in the form of finely scattered chromidia, come together. Their cytoplasms—and hence the chromidia— mingle together, and then separate again into the two individuals, each. Fig. 88. Arcella vulgaris. (A, B, after K. Hertwig, I'cstschr. Kupffer, 1899 ; C, after Swarczewsky, , 1908.) A, active phase, with two primary nuclei and a chromidial net; B, degeneration of primary nuclei and formation of secondary nuclei out of the chromidial net; C, mitosis of a secondary nuclexis. c, chromidia ; , primary nucleus ; , secondary nuclei. containing presumably a mixture of cliromidia from both conjugants. Out of these chromidia secondary nuclei are organized in a manner similar to that described above. In Coccidium schuhergi also, according to Schaudinn, the micro- gamete nuclei are produced from that of the microgametocyte by the passage of the chromatin of the latter out of the nucleus into the cytoplasm in the form of chromidia which rise to the surface of the cell, and there become aggregated into the microgamete nuclei. In Coccidium, Arcella, and still more definitely in Mastigella, therefore, during certain periods of the life history the chromatin is aggregat
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