XXII. On the placentation of the lemurs

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Abstract
Prior to the year 1871 naturalists were unacquainted with the form and structure of the placenta in the Lemurs. On the 14th August of that year M. Alphonse Milne-Edwards communicated to the Academy of Sciences of Paris a short memoir, entitled “Observations sur quelques points de l’Embryologie des Lémuriens, et sur les affinités zoologiques de ces animaux”. In this memoir M. Milne-Edwards stated that he had examined gravid uteri of Lemurs belonging to the genera Propithecus , Lepilemur , Hapalemur , and Chirogaleus with the following results. The chorion was almost entirely covered by villi, compactly arranged, constituting a kind of vascular cushion, and form­ing a placenta which enveloped, as with a hood, almost completely the amnion. He named the placenta “ placenta en cloche ,” or bell-shaped placenta. The villi were very bushy in the upper and mid portions of the ovum, and diminished gradually as they approached what he terms the cephalic pole, where they disappeared over a surface of some extent. The caduca uterina was very developed, and presented a corresponding disposition. He found a large sac between the chorion and amnion, which he regarded as the umbilical vesicle. He concluded that the placenta was constructed on a distinct type from that of all other mammals, but was further removed from that of Man, Apes, Bats, Insectivores, and Rodents than from that of the Carnivora,—“car si l’on suppose un instant le pôle caudal de l’œuf du chien envahi par les villosités du placenta, on a presque la réalisation des caractères spéciaux à l’œuf des Lémuriens.” In October of the same year M. Milne-Edwards reproduced this memoir, but with some important additions and modifications. In Propithecus , he said, the vascular cushion formed by the villi resulted from the confluence of a multitude of irregular cotyledons. The middle and upper portions of the mucous membrane exhibited numerous irregular anfractuosities, and the surface of the mucosa was hypertrophied, so as to form a caducous layer very analogous to that which, to a very feeble extent, adheres to the discoid placenta of the Apes, the Insectivora, and the Rodents. In the vicinity of the cervix uteri this hypertrophy gradually ceased, and the mucosa became quite smooth. The sac which in his first communication he described as the umbilical vesicle he now recognized to be the “allantois.” In the genera Lepilemur and Hapalemur the placenta was similarly constructed, but the villi were less compact. In Cheirogaleus the placenta was also bell-shaped, but extended over almost the entire surface of the ovum.

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