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Show 316 MR. W. A. FORBES ON THE [Apr. Cloaca of Casuariuspicticollis, adult male; viewed from before. A. Circular folds of mucous membrane, being the last remains of the Bursa. B. Bectum. b. Becto-cloacal valve. C. Cut surface of external sphincter muscle, c. Vesical sphincter. D. Urino-genital papilla?. E. Glandular pore. P. Penis. points also with the other Struthiones I am unable to say, as both the specimens I have dissected presented no trace of a bursa. Probably therefore in this, too, when adult the bursa disappears almost completely. I have mentioned above the singular differences shown by Signor Alesi to exist in the structure of the lymphatic follicles of the bursa of Rhea as compared with other birds. Although at first sight the relation of these parts in Rhea, Struthio, &c. seems so different from that which obtains in other birds, yet a little reflection will, I think, convince one that it is not so in reality. I have represented diagrammatically (figs. 8 and 9, p. 317) what I conceive to be the true relations of the parts in question, denoting the homologous regions in the two forms (Serpentarius as illustrating the normal type, Casuarius the abnormal one) by similar letters. If we imagine B in fig. 8 to lose the constriction at its aperture into D, and D to become proportionately deeper, we should have a form corresponding to fig. 9, in which B passes uninterruptedly and without |