An introduction to the study of the comparative anatomy of animals . trictiondivides the cell-body into two equal halves, which separate andform two new Paramecia. A swarm of Paramecia, wellsupplied with food, will continue to multiply by binary fissionfor many generations. Careful observation has shown that thedivisions take place two or three times every twenty-four hours,and that they will continue at this rate for some four or fivedays. But not longer. Towards the close of this period theoffspring of a single Paramecium, some four thousand innumber, become smaller and begin to show signs o
An introduction to the study of the comparative anatomy of animals . trictiondivides the cell-body into two equal halves, which separate andform two new Paramecia. A swarm of Paramecia, wellsupplied with food, will continue to multiply by binary fissionfor many generations. Careful observation has shown that thedivisions take place two or three times every twenty-four hours,and that they will continue at this rate for some four or fivedays. But not longer. Towards the close of this period theoffspring of a single Paramecium, some four thousand innumber, become smaller and begin to show signs of , if they are unable to conjugate, they undergo Digitized by Microsoft® CONJUGATION IN PARAMECIUM 197 degeneration and die. Similarly, if the food supply runsshort, the members of a swarm of Paramecia become weakand diminished in size ; but under normal circumstances theonset of degeneration is arrested by conjugation. Prior toconjugation the individuals move hither and thither in a rapidand excited manner as if in search of one another. After a. Fig. 42. Stages in the conjugation of Paramecium caudatum. A, Stage A, the micro-nucleus in each gamete preparing for division. B^ Stage B, the daughternuclei in each gamete dividing. C, Four micronuclei in each gamete. D,Three of the four micronuclei are disintegrating ; the surviving nucleus ineach gamete has divided to form o the male, and ^ the female pro-nucleus. Ej The male pronuclei crossing over. F^ Conjugation effected ;separation of the gametes and division of the combination nucleus. (AfterMaupas.) while they come together in couples and conjugate. Twoindividuals become attached together mouth to mouth, andare closely united by fusion or, at any rate, the intimate unionof their ventral cuticular surfaces. The two conjugatingindividuals or gametes are exactly like one another, though ofsmall size as compared with normal free-swimming forms. The Digitized by Microsoft® 198 COMPARATIVE ANATOMY usual length o
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