ELEMENTARY VITAL PHENOMENA 



201 



viduals apply themselves parallel to one another at their mouth - 

 openings (Fig. 82, 1., o), their masses of protoplasm join together to 

 form a bridge, and very characteristic changes in the nuclei begin. 

 As above remarked, ciliate Infusoria have two forms of nucleus 

 a macronucleus, or chief nucleus, and one or more micronuclei, or 



FIG. 82. Conjugation of Paramcecium in the various successive stages ; A*, macronucleus ; n k, 

 micronucleus. I. Beginning of conjugation. II. The micronucleus has divided twice in 

 succession. III. Three of the four portions of the micronucleus perish, the fourth divides 

 once more into a male m and a female w nucleus. IV. While the macronucleus is disin- 

 tegrating, the two male nuclei, 1m and 5m, become exchanged and unite with the two 

 female nuclei into a nucleus, V. t, which divides in turn into t' and t". VI. t' and t" divide. 

 VII. From this division arise the rudiments of the new macronucleus pt and the new micro- 

 nucleus nk'. The old macronucleus perishes. (After R. Hertwig.) 



accessory nuclei. During conjugation the macronucleus perishes, 

 disintegrating and dissolving in the protoplasm. If the Paramce- 

 cium be a form possessing one micronucleus, such as Paramcecium 

 caudatum, where the relations are simplest, the micronucleus in 

 each individual divides twice in succession, so that four partial 

 nuclei arise. Three of these likewise dissolve in the protoplasm, 



