1877. ] BURSA FABRICII IN BIRDS. olf 
had lived in the Society’s Gardens for eleven years. As a rule, the 
central cavity of the bursa becomes diminished and the communica- 
tion with the cloaca obliterated in the process of atrophy; and 
finally, in some cases at least, the whole organ completely disappears, 
losing its characteristic form and structure, and becoming fused with 
the tract of abdominal aponeurosis that covers the back wall of the 
alimentary canal, ultimately forming a flat riband-like, or round cord- 
like, ligamentous structure. Spangenberg observed the conversion of 
the bursa Fabricii into a round cord-like ligament in the Duck ; and 
Alesi has observed it (and described it minutely, with figures showing the 
histological changes that go on) in the Fowl. He sums up the pro- 
cess of atrophy in the last-named bird as follows :—The epithelium 
which covers the internal surface of the bursa becomes, as it were, 
invaginated into the thickness of the mucous layer, becoming pressed 
in between the lymphatic follicles. The connective tissue between 
the latter increases rapidly in bulk, and becomes full of numerous 
small oval corpuscles ; at the same time the follicles become absorbed, 
and the whole of the bursa becomes obliterated and fused with part 
of the abdominal aponeurosis. The epithelium gradually becomes 
confined to certain irregular tracts in the thickness of the mass of 
connective tissue ; but even these disappear finally. The process of 
atrophy in the other species which he observed is essentially the 
same as that in the Fowl. 
I now proceed to describe the general characters of the bursa 
Fabricii in the groups of birds I have examined. In the Passeres 
it is usually small, pyriform, with a small opening and glandular 
walls without ridge-like elevations on the interior. It seems to 
disappear completely in adult birds. In the Rhamphastide : dis- 
Fig. 3. 

° Cloaca and Bursa of Geococcyx affinis. 
The cloaca is cut short and laid open from before. The narrow peduncle of the 
bursa is supposed to be seen through the cloaca. @. “ Vesical sphincter.” 
b. Bursa. c. Opening of same. 4, d’. Ureter and opening. ¢, é’. Vas 
deferens and opening. 
appears in the adult, only leaving a small pore to mark its place of 
opening. In the Cuculide it presents a very characteristic shape, 
the peduncle being long and thin, and the extremity club-shaped, 
