ABSTRACT
Lesser galago embryos resemble marmoset embryos in terms of size and age as contrasted to the embryos of man, rhesus monkey, and baboon. The primitive streak appears at 25 to 28 days in the lesser galago and marmoset but at 17 days in the baboon and rhesus monkey and 16 days in man. By stage 23 the lesser galago embryo is 14.0 mm long, compared to 30.4, 27.5, and 26.5 mm in man, rhesus monkey, and baboon, respectively. Despite these differences, their external and internal appearances follow the same pattern of development as the other primate embryos. The lesser galago, as contrasted to baboon and rhesus monkey, has a well-developed vomeronasal organ very comparable to that seen in the human embryo. At stage 23 the embryos of man, baboon, rhesus monkey, and lesser galago have distinctly different external features. By stage 23, many of the species-specific internal features of the lesser galago are present. It is noteworthy that the characteristically elongated tarsus of the lesser galago is not seen until about midterm. Left lateral (above) and dorsal (below) aspects of a reconstruction of a Carnegie stage 11 lesser galago embryo. A = cut edge of yolk sac; B = cut edge of amnion; C = allantois; D = coelom; E = posterior neuropore. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781351069939/5bbd806d-0715-46b3-b0f7-7252d28d5864/content/fig_49.jpg"/>
