OCR Text |
Show 318 MR. FORBES ON THE BURSA FABRICII IN BIRDS. [Apr. 1 7, Testuclinata can be in no way related to that under discussion. The anal glands of Mammals, again, open externally on the skin, and are in fact cutaneous glands. The prostate and glands of Cowper are purely male glands, and probably play some important function in the act of reproduction ; so that they can hardly well correspond to an organ that is common to both sexes, and only proportionally developed in the young. It would be premature to accept Buschke's views without further observations on the subject. On the other hand, as pointed out by Signor Alesi, a lymphatic organ, constructed on a similar principle, but in a simpler form, exists in the patches of lymphatic follicles (which do not, however, in this instance project outside the mucous membrane of the intestine) in the appendix to the caecum of the rabbit (described by Frey, ' Untersuchungen iiber die Lymphgefasse des Darmkanales,' Leipzig, 1863). An organ still more closely corresponding in its general shape and position with the bursa Fabricii is the sac like pouch which opens into the dorsal wall of the cloaca in many Elasmobranchs1. The glands of this, however, differ in structure from those of the bursa Fabricii; so that at present it seems to me that we can assign no very definite analogue or homologue for the latter, but that it is a glandular outgrowth of the cloaca peculiar to birds. In conclusion, I may briefly capitulate the chief conclusions arrived at in this paper. (1) That the bursa Fabricii exists in both sexes, and probably in all species, of birds. (2) That it is most developed in young birds, but becomes atrophied and more or less obliterated in adults, the period, however, of the commencement and conclusion of this process differing greatly in various birds. In some it probably persists, though in a state of functional inactivity, throughout life. (3) That in the majority of birds the bursa is a moderate-sized or small sac, that opens by a narrow aperture on the dorsal wall of the cloaca into the lowest " chamber " of that organ. (4) That in the Struthious birds, on the contrary (the state of Apteryx as regards these points being doubtful), the cloaca opens into the bursa by a posterior aperture, owing to the fact that the bursa is not constricted off at the neck, but is commensurate in extent with the third or outer chamber of the cloaca, the two being united into one. This condition, however, is only to be found in young birds. (5) That the bursa is a glandular organ, of which lymphatic follicles are the essential constituents, but has no exact homologue in other classes of Vertebrata. 1 Signor Alesi, in his paper, s. c, alludes to this pouch as being ventral in position, which it certainly is not. It is figured in Squatina vulgaris by Gegenbaur (Vergl. Anatomie, fig. 267 c, & p. 798). It is absent in Chimcera. Leydig has described its structure ('Beitrage z. microscop. Anat. u. Enlwickel. der Eochen u. Haie,' Leipzig, 1852), and found that it consisted of collections of glands similar to the glands of Brunner. |