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Updated: May 25, 2025
The European heartsease, from which our garden-pansies have been chiefly derived, will serve as an example. The garden-pansies are a hybrid race, won by crossing the Viola tricolor with the large flowered and bright yellow V. lutea. They combine, as everyone knows, in their wide range of varieties, the attributes of the latter with the peculiarities of the former species.
During the whole of this time there are no embryos in the uteri, and therefore it might be urged absorption of hormones from the embryos cannot be the cause of the persistence of corpora lutea in pregnancy. But it seems to me that a complete answer to this objection is supplied by the peculiar relations of the embryos to the pouch in Dasyurus and other Marsupials.
Besides the lutea, there are some other species, nearly allied to tricolor, as for instance, cornuta, calcarata, and altaica, which are combined with it under the head of Melanium as a subgenus, and which together constitute a systematic unity of undoubted value, but ranging between the common conceptions of genus and species.
O'Donoghue, however, concludes from a study of the Marsupial Dasyurus that the stimulus which upon the milk glands proceeds from the corpora lutea in the ovary. In this animal changes in the pouch occur in pregnancy, which are doubtless also due to hormone stimulation, but which we will not consider here. Journ. Mic.
These facts alone would be sufficient to disprove the theory that the corpora lutea are organs producing a secretion whose function is to cause the attachment of the embryo to the uterine mucosa.
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