A contribution to the anatomy and development of the venous system of didelphys marsupialis (L). Part II, development

Abstract

A number of publications have appeared, especially the monographs of Selenka, 86-7 and 91, and Semon, 94, in which have been described the arrangement of the blood vessels in the extra-embryonic vascular area of marsupials.So far as known to the writer, however, the only actual contributions that have been made to the development of the intra-embryonic venous system of this group of mammals are one by Broom, 98, and a preliminary notice by the writer, 02.The publication of the present paper (Part 11) has been unavoidably delayed, owing to the writer's inability to obtain embryos sufficiently young to show the earliest stages in the development of the postcaval vein.These early stages have, unfortunately, not yet been obtained, and were it not for the circumstance that so little has been published upon the development of the veins of marsupials, an apology would be due for presenting what must necessarily be an incomplete account.I n writing this paper the writer has fully borne in mind the danger involved of drawing conclusions from an incomplete series, and, in the case of Didelphys, the danger is especially great on account of the variable character of its venous system.A complete account of the development of the veins of Didelphys, especially of the variations of the postcava, necessitates not only a complete series of embryos and pouch young, but a number of examples from each stage as well.Such an The publication of this paper in two parts, one dealing with the Anatomy (Part I) and the other, o r present paper (Part II), with the Development of the venous system, was unavoidable and it is, therefore, to be hoped that the frequent references made in the following pages to Part I will not prove too great a source of confusion or inconvenience to the reader.