190 EDWARD A. BOYDEN 
point of origin of the group of glandular outgrowths that con- 
stitute the prostate gland is rather remote, embryologically, 
from that of the bursa; also that the prostate develops much 
later and is radically different in its histological nature. Physi- 
ologically it becomes functional with sexual maturity, at the 
time when, as Jolly has shown, the bursa degenerates. 
The only other vertebrate structures thus far proposed, which 
in any way meet the requirements of the homology, are the anal 
sacs (bursae anales) of turtles. Gadow, in the Cambridge 
Natural History Series, 1909, describes these organs in the adult 
as highly vascularized, thin-walled sacs which are incessantly 
filled and emptied with water through the vent, and act as im- 
portant respiratory organs. Forbes, in. 1877, objected to the 
comparison of these sacs with the bursa of Fabricius on the ground 
that they were paired, lateral structures. Wenckebach also 
saw this objection, but considered that the anal sacs were the 
only diverticula which in any way could be compared in point of 
origin with the bursa, and, in view of the almost total ignorance 
regarding the embryology of the sacs, held that the objections 
to the comparison should not be conclusive. During the last 
year a graded series of models of the turtle cloaca have been 
made in this laboratory by R. F. Shaner as a part of an anatomi- 
cal study of the 9.5-mm. Chrysemys embryo. As a result of 
this study he is of the opinion that the anal sacs arise from a 
single median diverticulum (fig. 3, an. s.).. Through the courtesy 
of Doctor Shaner, I have had the pleasure of studying the models 
upon which his paper is based and concur in his opinion. Another 
feature which at first seemed to favor the comparison between 
the bursa and the anal sacs is the striking similarity of the proc- 
ess by means of which the outlet of each diverticulum is taken 
over by the proctodaeum. In each case lateral expansions of 
the proctodaeum (fig. 39) grow down across the flanks of the 
cloaca until they establish communication with either the bursa 
or the anal sacs. But the description of the saurian cloacas 
in the Fleischmann series seems to indicate that this invasion 
of some point of the urodaeum by the lateral proctadaeal in- 
vagination is not restricted to reptiles equipped with anal sacs, 
