The cell in development and inheritance . age-nucleus of the ovum, then gives rise by division to both macronucleiand micronuclei of the offspring of the conjugating animals (Fig. 109). These facts may be illustrated by the conjugation of ParamoEciiimcmidatum, which possesses a single macronucleus and micronucleus,and in which conjugation is temporary and fertilization mutual. Thetwo animals become united by their ventral sides and the macronu-cleus of each begins to degenerate, while the micronucleus dividestwice to form four spindle-shaped bodies (Fig. no. A, B). Three ofthese degenerate, fo
The cell in development and inheritance . age-nucleus of the ovum, then gives rise by division to both macronucleiand micronuclei of the offspring of the conjugating animals (Fig. 109). These facts may be illustrated by the conjugation of ParamoEciiimcmidatum, which possesses a single macronucleus and micronucleus,and in which conjugation is temporary and fertilization mutual. Thetwo animals become united by their ventral sides and the macronu-cleus of each begins to degenerate, while the micronucleus dividestwice to form four spindle-shaped bodies (Fig. no. A, B). Three ofthese degenerate, forming the corpuscules de rebut, which playno further part. The fourth divides into two, one of which, thefemale pronucleus, remains in the body, while the other, or malepronucleus, passes into the other animal and fuses with the femalepronucleus (Fig. no, C-H). Each animal now contains a cleavage-nucleus equally derived from both the conjugating animals, and thelatter soon separate. The cleavage-nucleus in each divides three 1 cy:?. Fig. no. — Conjugation of PanwKBciiim caudatum. [A-C, after R. Hertwig; D-K, afterMaupas.] (The macronuclei dotted in all the figures.) A. Micronuclei preparing for their first division. B. Second division. C. Third division;three polar bodies or corpuscules dc rebut, and one dividing germ-nucleus in each animal. of the germ-nuclei. £. The same, enlarged. /•. Fusion of the germ-nuclei. G. Thesame, enlarged. //. Cleavage-nucleus, (n) preparing for the first division. /. The cleavage-nucleus has divided twice. 7. After three divisions of the cleavage-nucleus; macronucleusbrealcing up. A. Four of the nuclei enlarging to form new macronuclei. The first fission soontakes place. O 225 226 FERTILIZATION OF THE OVUM times successively, and of the eight resulting bodies four becomemacronuclei and four micronuclei (Fig. no, H-K). By two suc-ceeding fissions the four macronuclei are then distributed, one to eachof the four resulting indiv
Size: 1266px × 1974px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, booksubjectcells, bookyear1902
