. A manual of zoology. Zoology. 206 The nuclear relations are extremely interesting in that there are two nuclei physiologically unlike. The larger of these {nucleus of older writers, macromtcleus) is a large oval, rod-like, or spiral body, readily and deeply staining with microscopic stains, and sur- rounded with a membrane. It appears to control all the common / vital functions of the animal (motion, feeding, etc.). Beside it or in a depres- sion in it is the much smaller micro- nuclens (nucleolus or paranucleus of older authors) which stains less deeply and only plays a part in r
. A manual of zoology. Zoology. 206 The nuclear relations are extremely interesting in that there are two nuclei physiologically unlike. The larger of these {nucleus of older writers, macromtcleus) is a large oval, rod-like, or spiral body, readily and deeply staining with microscopic stains, and sur- rounded with a membrane. It appears to control all the common / vital functions of the animal (motion, feeding, etc.). Beside it or in a depres- sion in it is the much smaller micro- nuclens (nucleolus or paranucleus of older authors) which stains less deeply and only plays a part in reproduction. In all sexual processes it comes to the front and can be called the sexual nucleus. Multiplication of Ciliata occurs by binary fission (fig. 145); more rarely, and then only in the encysted condition, by division into numerous (up to 64) parts. Budding is known in the Peritricha and Suctoria. First the micronucleiis divides ^ ,,- _ . ,. mitotically, and then the macronucleus Fig. 145.—ParamcEcnim aurelia ^ in division. ?c, macronucleus; separates by elouffation and construction. ?i'., micronuclei; o, cytostonie . of tiie separating individuals. The old cytostome persists in the anterior At £' an early stage of division «» . i of cytostome. offspring, but otten an outgrowth from it (fig. 145, 2, o') passes into the posterior half and develops into a new mouth. The periods of fission are interrupted from time to time by tlie sexual process of conjugation, which will be described as it occurs in Paramcecium (fig. 146). Two individuals touch at first in front, and then by their whole ventral surfaces, so that their cytostomes come together. In the neighborhood of the latter a jilasma bridge connects the two. Later the individuals separate. While these easily observable external processes are occurring there is a com- plete modification of the nuclear apparatus in the interior. The macronucleus increases in size, and breaks into small jiortious which disappear with
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