The Structure of the Mammalian Csophagus. 39 
principal orders both of marsupials and placentals contain individuals 
wholly lacking in cesophageal glands indicates that these structures 
have been developed independently in the different orders in response 
to needs that have arisen as result of food specialization. The alterna- 
tive hypothesis that they were originally present in all mammals 
and that they have disappeared from some is scarcely worth considera- 
tion in view of the general absence of similar glands in lower verte- 
brates. 
In man alone is there any indication that the cesophageal glands 
are disappearing. Here the great variability in number of the glands 
and the constant presence of cyst formation and stasis of the secre- 
tion and atrophy of the glandular cells might be taken as an indica- 
tion of a disappearing structure. 
Tn conclusion I desire to express my thanks to Prof. R. R. Bensley 
for valuable suggestions during the course of this investigation. 1 
desire also to thank Miss Katharine Hill for the accompanying 
drawings. 
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