Three human embryos were used in the study. The yolk sac and yolk stalk on one of them were well preserved. An observation on main external characteristics of embryos and measurements were made with stereomicroscopy. There were some discripances on the curve of the body on the 'C' shaped embryo (estimated age 28 to 53 days), which might be a result of the difference in the measurements of crowm-rump length (CRL). Therefore, we believe that CRL of embryo in this period ...
