318 MR. FORBES ON’ THE BURSA FABRICII IN BIRDS. [Apr. 17, 
Testudinata 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 de- 
veloped in the young. It would be premature to accept Huschke’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 cecum of the rabbit (described by Frey, ‘ Untersuchungen 
iiber die Lymphgefiasse 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 Elasmobranchs'. ‘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 out- 
growth 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 atro- 
phied 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. ¢., alludes to this pouch as being ventral in 
position, which it certainly is not. It is figured in Sguatina vulgaris by Gegen- 
baur (Vergl. Anatomie, fig. 267¢, & p.798). It is absent in Chimera. Leydig 
has described its structure (‘Beitrage z. microscop. Anat. u. Entwickel. der 
Rochen u. Haie,’ Leipzig, 1852), and found that it consisted of collections of 
glands similar to the glands of Brunner. 
