188 EDWARD A. BOYDEN 
function is not peculiar to the bursa, but is an attribute common 
to the mesenchyma of certain other organs. He does, however, 
propose a specific function when he suggests that the bursa 
contributes substances to the organism which bear a causal re- 
lation to the inception of sexual maturity. He bases this theory 
on two facts: 1) that the maximum development of the bursa 
is attained at the time when spermatogenesis is just getting under 
way; 2) that involution of the bursa corresponds exactly with the 
appearance of sexual maturity, as measured by the sudden in- 
crease of testicular weight and the appearance of ripe sperma- 
tozoa. Before accepting this theory, however, one would like 
to know to what extent the precocious involution, which Jolly 
produced in the bursa by means of the x-ray, affected the differ- 
entiation of the testis. ‘That some such line of experimentation 
as this would be profitable seems almost certain when we consider 
the history of such organs as the thymus. For it is far from in- 
conceivable that the bursa may also be a glandular organ in 
process of transformation into an endocrine gland, if it has not 
already arrived at that estate. 
The phylogenetic interpretation of the bursa is equally obscure. 
An extensive number of investigators distributed over three 
centuries have tried to solve this problem and during this period 
have proposed numerous hypotheses, all of which have been . 
rejected (see Retterer, 13 b, for list). Forbes, after examining 
the bursae of over ninety species of birds and covering the litera- 
ture, came to the conclusion that the bursa was a glandular 
outgrowth of birds sui generis. Wenckebach limited the problem 
by establishing the entodermal origin of the bursa, thus making 
obligatory the origin of homologous structures (with which it 
is to be compared) from the dorsal wall of the vertebrate cloaca. 
Its origin has been still further limited by this paper to the area 
between the cloacal end of the caudal intestine and the anal 
plate. 
These limitations render untenable the hypothesis put forth 
by Stieda (80) that ‘“‘the bursa develops from the epithelial 
elements which originally belong to the caudal intestine.” Equal- 
ly untenable is the modification of this theory, presented by 
a 
