ABSTRACT
Phillips 17 described 36 marmoset embryos and arranged them into Carnegie stages 7 to 11, 13 to 17, 19 and 21. Marmosets commonly have twins which are enclosed in a common chorion, but each twin has its own discoidal placenta. However, the placental vessels are connected by extensive vascular anastomoses. In the cases of stages 7 and 8, the embryo was not identifiable visually, and the conceptual sac was serially sectioned. Stage 7 is regarded as the beginning of the embryonic period, and the trilaminar embryonic disc has an early primitive streak. The stage 8 embryos have a trilaminar disc with a notochord and primitive groove. The minimum and maximum ages were: stage 7, 25 to 28 days; stage 8, 42 to 49 days. Only one stage 9 embryo was recovered, but it had not yet developed any somites. Its minimum and maximum ages were 55 to 59 days. One set of twin embryos of stage 10 were recovered. They had seven pairs of somites and prominent neural folds. Both had marked cranial and dorsal flexures. Their minimum and maximum ages were 51 to 59 days.
