ON THE PLACENTATION OF THE HARBOR PORPOISE (PHOCÆNA PHOCŒNA (LINNÆUS))

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Abstract
Examination of a rather well-preserved specimen of one of the smallest species of whales (P. phocoena) demonstrates that near term the placenta is diffuse and is of the epithelio-chorial type. Although diffuse in character, the chorion can be divided at this stage into 2 rather well-defined areas; the first, an area of intimate interdigitation of branching villi and proliferated endometrium corresponding in the main to the region of allantochorionic fusion; the second, an area of stunted villi and reduced endometrium corresponding roughly to the area of amnio-chorionic fusion. These areas can be related to some extent to the allantoic blood supply, which is much more profuse in the region of the allantochorion than in the region of the amniochorion. In spite of the fact that the branching chorionic villi are intimately interlocked in the allantochorionic area with crypts of the uterine mucosa, the endometrium, as well as the chorion, retains its complete integrity by virtue of the survival of intact epithelial coverings. In the case of the endo-metrium, the epithelium is cuboidal in the fundic parts of the endometrial crypts, whereas it is flattened in the outer and more extensive parts of the crypts. The chorionic epithelium, on the contrary, although forming a complete investiture of the villi, is interpreted as being syncytial in character. Thus the placenta is of the epi-thelio-chorial type, as described in the sow, horse, tapir, hippopotamus, camel, Manis, and the lemurs. The interlocking of chorionic villi and endometrium is, however, much more complex than in the sow, being more like that described in the horse. Whether the attenuated endometrium in the amniochorionic area of the porpoise bears close analogy to the horse, in which widespread degeneration of the endometrium is said to occur in the 4th and 5th mos., cannot be ascertained without access to further stages of the porpoise. Be that as it may, the porpoise placenta does not appear to be of the syndesmochorial type which occurs typically in many ungulates. It appears inconceivable, however, that at parturition the fetal and maternal tissues, which are intimately interlocked in the area of the alantochorion, are destined to separate without a certain amount of damage to the chorion and endometrium. Either the endometrium must be torn away to some degree or the chorionic villi must be torn off and retained to a certain extent. A separation without trauma to the tissues appears unlikely.

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