Fig. 25. Matdration and Fertilization of the Egg of the Mouse. A, first polar body and second maturation spindle ; B, second polar body and maturation spindle; C, entrance of the spermatozoon into the egg; D-G, successive stages in the approach of egg and sperm nuclei ; H, formation of chromosomes in each germ nucleus ; I, first cleavage spindle showing chromosomes from egg and sperm on opposite sides of spindle. (After Sobotta.)
grows thinner and finally disappears altogether, leaving the chromo- somes in the equator of the spindle (Figs. 23 F, 24 E and F, 25 I).
Each of the chromosomes then splits lengthwise into two equalparts, and in the splitting of the chromosomes it is sometimes possible