The natural history of the nine-banded armadillo of Texas / by H.H. Newman.

  • Newman, H. H.
Date:
1913
Catalogue details

Licence: In copyright

Credit: The natural history of the nine-banded armadillo of Texas / by H.H. Newman. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    these villous regions expand they come into contact at their margins and apparently fuse into a lobate zone, which had been called a compound zonary placenta. Finally the zone separates along the dorsal and ventral lines to form two lateral notched discoid placentae, to which we need scarcely apply a name. It is obvious that there is nothing to be gained by attempting to classify sncli a placental complex or by comparing it with those of other groups of mammals, for the peculiar conditions seen here are obviously merely very special adjustment to the peculiar conditions arising from polyembryonic development within a single chorion. The foetuses after they have once been separately outlined are distinct, com- plete units and are associated scarcely more closely than are the embryos of other forms of mammals where sev- eral individuals develop simultaneously in a single uterus, for they have their own separate amnia and separate placentation, and there is absolutely no admixture of foetal blood. Without further burdening the reader with an elabora- tion of embryonic details and relations we may briefly sum- marize the situation in-so-far as the question of specific polyembrvony is involved. The ovogenesis is normal; a single egg is fertilized by a single spermatozoon; the cleavage is apparently normal and gives rise to a blasto- dermic vesicle similar to that of other mammals, espe- cially the rodents; germ-layer-inversion affords an easy mechanism for producing several embryos in a single chorion, for the quadruplets arise by means of dichot- omous budding of the inner ectodermic vesicle without affecting the enveloping membranes of the vesicle, which form the common chorion; the subsequent embryonic development of the several embryos is as independent as it can be under monochorial conditions, since each indi- vidual has its own separate amnion, allantois, umbilicus and placenta. This in brief is the polyembryonic situa- tion, a consideration of which offers for solution several problems peculiar to the material. What are the physio-