Carnegie Stage 6

Introduction

Stage 6 embryos are in the presomite period and have an estimated postfertilization age of 16 to 21 days and a greatest length of approximately 0.3 mm. When the gastrulation (primitive) streak is present in the caudal part of the specimen it is sometimes classified as Stage 6b. Similar specimens without a gastrulation streak are then classified as Stage 6a. Chorionic villi and the amniotic cavity and secondary umbilical vesicle (yolk sac) are evident. Embryonic endoderm is present for the first time.