Reproduction by Binary and Multiple Fission in Gigantomonas*

Abstract

SYNOPSIS. Gigantomonas usually exists in the multinucleate stage. Hence, multiple fission is more common than binary fission. In its flagellate as well as its aflagellate state it is always an amoeboid cell which possesses from one to several large, clear pseudopodia. Fairly often in the multinucleate, as well as the uninucleate, stage no extranuclear organelles are present except large plain centrioles, two of which are always closely associated with each nucleus. During nuclear reproduction four centrioles, two old ones and two new ones, are always present with each nucleus. During all nuclear reproductions, regardless of the number of nuclei present, extranuclear organelles, such as flagella, axostyle, undulating membrane, and costa when present are discarded. If they are renewed, it is by the new centrioles at the same time that the old ones produce new central spindles, two always cooperating in the process. Thus, Gigantomonas, like other genera of the Devescovinidae, the family to which it belongs, never has for each nucleus present more than one set of extranuclear organelles, a characteristic which Devescovinidae and Lophomonadidae have in common. It is the only genus of Devescovinidae without a parabasal body.Owing to the liquidness of the cytoplasm, the central spindle, which becomes very long indeed, often extends beyond the cytoplasm and thus pushes the nucleus fastened to this end of it completely out of the cell. Mainly because of this situation, multinucleate forms with an odd number of nuclei occur often; otherwise the nuclear numbers would be 2, 4, 8, 16, 32, etc., because, no matter how many nuclei are present, they all reproduce simultaneously or nearly so.An unusual situation occurs in which Gigantomonas ingests and digests a small species of Holomastigotoides, while several hundred individuals of the latter become attached to and destroy Gigantomonas.