Abstract
Employingthe albino mouse, MUS musculus L., derived from the Carnegie Institution strain, as the material, the processes of maturation of the egg and the phenomena of fertilization were cytologically investigated.The first maturation division of the egg is completed prior to ovulation within the ovarian follicle. After the first polar body is extruded, the chromosomes remaining in the egg are immediatelydrawn into the equatorial plate forming the metaphase spindle of the second maturation division. In this condition the egg undergoes ovulation. Fertilization occurs in the upper portion of the oviduct. Shortly after insemination, the second division advances in its course and as a result the formation of the second polar body is brought about. Therefore, stages subsequent to the metaphase of the second division take place only after the entry of the spermatozoon into the egg. Insemination is a necessary antecedent to the second maturation division. After being completely formed into the spherical body, the female and male pronuclei are alike in appearance but distinguishable only by their size.
Detailed accounts on this subject will appear in the Journal of Science, Hokkaido Imperial University, Series VI, Zoology, Vol. 7, No. 4.
