The morphology and timing of fertilization and early cleavage in the Mongolian gerbil and Deer mouse.

Ovulation, fertilization and early cleavage have been investigated in few myomorph rodents and in only two members of the family Cricetidae. The Golden hamster (subfamily Cricetinae: Mesocricetus auratus) was studied by Graves (1945), Venable (1946a, b), Ward (1948), Strauss (1956) and Harvey, Yanagimachi & Chang (1961), using fixed and stained materials; and Austin (1956a), Samuel & Hamilton (1942) and Hamilton & Samuel (1956) examined the living eggs. The effects of delayed fertilization were investigated by Chang & Fernandez-Cano (1958) and Yanagimachi & Chang (1961). The Field vole (subfamily Microtinae: Microtus agrestis) was studied by Austin (1957). The present paper deals with the processes of fertilization and cleavage in the Mongolian gerbil (subfamily Gerbillinae: Meriones unguiculatus) and the Deer mouse (subfamily Cricetinae: Peromyscus maniculatus bairdii).