Weight of Mouse Embryos 10-18 Days After Conception,a Logarithmic Function of Embryo Age.

Abstract

The following methods were adopted in the endeavor to provide the optimum developmental conditions and to reduce the variability of the mouse embryos as far as possible. The mothers were self-colored, intense, brown-agoutis, F₁ hybrids between two highly inbred, pedigreed strains, the females from the Bagg albino and the males from the Storrs-Little, characterized by pink-eyed dilute brown self-color. The albino grandmothers at conception were over ten weeks old and had not nursed young for at least three weeks; the mothers were nursed in litters that had been cut down to six at birth; they were weaned at four weeks and held in large mating boxes, not more than six to a box, until over three months old before mating was first permitted. The fathers of the embryos weighed came from the inbred line 89,-self-colored, intense, brownagouti; they were kept individually in small boxes. This type of mating gives embryos that may be called triple hybrids; they bear the maximum heterozygosity and hence show the minimum amount of segregation. When matings were desired each male was placed with the females in a certain box for one hour and the females then examined for vaginal plugs as evidence of copulation. Each female with a plug was immediately given a small box to herself until the hour assigned for weighing the embryos; she was killed at some exact multiple of 24 hours from the end of the hour she was with the male.

The membranes and placentae wen5 removed with the aid of a binocular microscope; for embryos of 10, 11 and 12 days this was done in Locke's solution. As soon as a dissection was finished the excess fluid was blotted off and the embryo placed in a glass ring of appropriate size between cover glasses, or in a small weighing bottle (18-day embryos), and carried at once to the balance pan.