. A manual of zoology. Zoology. 11)4 PROTOZOA The periods of tission aie interrupted from lime to time l>v the sexual process of conjugation, whicii will be descrilied as it occurs in Para Dim in in (tig. 151). Two indivitluals touch l)y their whole A-entral surfaces, so that their cytostomes come together. In the neighborhood of lire latter a bridge of ]>rotoplasm connects tire two animals. Later the individuals separate. \\'hile these easily obser\a,ble external processes are occurring there is a complete modilicalion of the nuclear a|)paratus in the interior. The macronucleus increase
. A manual of zoology. Zoology. 11)4 PROTOZOA The periods of tission aie interrupted from lime to time l>v the sexual process of conjugation, whicii will be descrilied as it occurs in Para Dim in in (tig. 151). Two indivitluals touch l)y their whole A-entral surfaces, so that their cytostomes come together. In the neighborhood of lire latter a bridge of ]>rotoplasm connects tire two animals. Later the individuals separate. \\'hile these easily obser\a,ble external processes are occurring there is a complete modilicalion of the nuclear a|)paratus in the interior. The macronucleus increases in size, and breaks into small portions which disappear witliin the Ih-st week after copulation (probably by absorption), and give place to a new irucleus derived from the niicronucleus. At the beginning of copulation the nricromicleus becomes s])indle-sha])ed, divides and repeats the process, the result being the formatioir of four spindles in each animal, three of which break down, thus recalling the polar globules in the maturation of the egg (p. 1,13). The fourth or principal spindle places itself in the neighborhood of the cytostome at right angles to the surface and divides into two nuclei, the superhcial being called the wandering or male nucleus, the deejier, the stationary or female nucleus. The male nuclei rr^^!'^, ^O of the two copulating animals are exchanged, tra\ersing the proto- plasmic bridge in their course (III). Both male and female nuclei usually become spindle-shaped, and the im- migrant male spindle fuses with the female spindle, forming a sijigle spindle of division. At last, after processes which differ in tire various genera, the division spindle pro- duces (usuall)- by indirect means) two nuclei, one of wliich l)ecomes the new macronucleus, the other the new niicronucleus. In a comparison of the fertiliza- tioir of the Metazoa, the female nucleus corresponds to the egg nucleus, the male nucleus to that of the spermatozoa. As iJie fusion of egg and sp
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectzoology, bookyear1912
