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Show 1877.] BURSA FABRICII IN BIRDS. 317 constriction into D, the cavity B D thus formed receiving the aperture of C. In such a form as Plotus, where the opening is but very slightly constricted, we have a type connecting the two extremes; and I have seen Rhea in a stage very similar to that mentioned above in Cygnus olor. In confirmation of this view as to the true relation of these parts, in the Ostrich &c. the lower part of the bursa, in the region corresponding to D in figs. 8 and 9, is not glandular (vide fig. 6, p. 315, where the non-glandular part of the bursa is seen beneath pores H H'). Fig. 8. Fig. 9. Diagram showing two chief Types of Development of the Bursa Fabricii. B. Bectum. B. Bursa. C. Cloacal chamber. D. Lowest chamber of " cloaca." d. Openings of urino-genital ducts. With regard to the function and homologies of the bursa Fabricii, great differences have prevailed amongst authors. Thus Milne- Edwards says1, " Fabrice d'Acquapendente, a qui Ton doit la decouverte de cette bourse, la considerait comme un reservoir seminal, tandis que d'autres naturalistes2 la regardent comme une vessie uri-naire. Perrault et quelques auteurs modernes3 y voient 1'analogue des glandes anales des Mammiferes, et Geoffr. St.-Hilaire TassimuV aux glandes du Cowper4; enfin, M . Martin St.-Ange la compare a la prostate." Emil. Huschke, in the paper mentioned above, has studied its development, and, after a comparison of the organs of similar appearance, is inclined to consider it as the primitive urinary vesicle of the Wolfian bodies, from the fact that the ducts of this gland take origin from just that part of the cloaca which afterwards assumes the form of the bursa. Harvey and others have sufficiently disproved Fabricius's ideas as to its serving as a spermo-theca; nor can the bursa be regarded as a urinary bladder,-first, because it is not devoted to containing the urine; secondly, because in other Sauropsida and also in the Mammalia the urinary bladder is ventral, not dorsal, in position. For a similar reason, as well as from the fact that they are paired organs, the " bursee anales" of the 1 Phvs. et Anat. Comp. vol. viii. p. 514. 2 E.g. Berthold, Acad. Cass.-Leop. Nova Acta, xiv. p. 917, 1828, and Geoffroy St.-Hilaire, Mem. du Museum, 1823, t. ix. p. 394. 3 E. g. Cams, ' Zootomia.' 4 Tiedemann, Anat. der Vogel,' 1810. |