Ultrastructural changes in preimplantation rabbit embryos.

Follicular oocytes and penetrated eggs of several mammalian species have been the subject of numerous electron microscope studies (rat: Sotelo 1959, Sotelo and Porter 1959, Franchi 1960, Odor and Renninger 1960, Szollosi and Ris 1961, Guinea pig: Anderson and Beams 1960, Adams and Hertwig 1964, Austin 1965. Barron and Franklin 1968. cat: Liss 1964. man: Stegner and Waternberg 1961, Zamboni et al., 1966, Baker and Franchi 1967, Baca and Zamboni 1967 and rabbit: Blanchette 1961, Merker 1961, Hadek 1963, Zamboni and Mastroianni 1966). However the segmentation process has been studied in only two laboratory animals: the rat (Izquierdo and Vial 1962, Schlafke and Enders 1963, and Mazanek 1965) and the mouse (Hillmann 1967). There is also a brief report by Enders and Schlafke (1965) in which several preimplanting mammalian embryos were examined and in which a number of species differences were found. While segmentation in the rabbit has been the subject of numerous metabolic and physiological investigations (Adams 1958, Fridhandler 1961, Chang 1966, Daniel 1967), our knowledge of its ultrastructure during this process has received only limited attention (Austin 1965). It is the purpose of this article to describe the cytoplasmic and nuclear changes which occur in the rabbit embryo from the two blastomere stage to the early blastocyst.