52 TRANSACTIONS OF THE [Derc. 12: 
can alone explain such conditions as the identity of the dentition 
in Cynoidea and Arctoidea, whereas in another part of the same 
organic system we meet with the transition from the compara- 
tively highly developed and complicated czecum of the former to 
the simple ileo-colic junction of the latter. In respect to spe- 
cific peculiarities of the condition as found in Procyon lotor, a 
few facts deserve mention. 
The transition from large to small intestine is marked by a 
difference in the calibre as well as in the structure of the wall of 
the tube. For a distance of about 15cm. before the ileo-colic 
junction is reached, the distal portion of the ileum presents a 
series of irregularities in calibre. A number (2-3) of constric- 
tions at a few em. interval occupy this terminal portion. They 
are associated with an increase in the circular muscular fibres of 
the gut, which appear somewhat aggregated in these situations, 
but the narrowing of the lumen remains after complete relaxa- 
tion and distension of the intestine. 
It appears reasonable to bring this condition into relation 
with the complete absence of an ileo-colic valve. Some form of 
mechanical separation of the lumen of the canal between large 
and small intestine seems to belong to forms in which there is 
an absence of cecum and ileo-colic valve. 
In Manis macrura this appears to be accomplished by the 
abrupt bend of the tube at the point of transition and may serve 
to render a return of contents from large to small intestine more 
difficult. 
In Procyon the constrictions and the accompanying muscular 
arrangements in the terminal part of the small intestine may 
perform the same function. As regards the colon, a thicker 
circular band of muscular fibres at the ileo-colic junction itself, 
‘undoubtedly acts in the same way, although it does not impress 
itself on the lumen of the canal as a permanent fold in the 
relaxed and distended condition. 
An increased bearing of the convex margin of the large in- 
testine may fairly be taken to represent the cecal disposition. 
Several lines of investigation appear to promise results in this 
connection. 
The embryological differentiation of large and small intestine 
in Procyonide may afford valuable information. It seems 
probable that the ileo-colic junction in this form represents the 
highest grade of the process of reduction and diminution ob- 
served in so many instances, that of our own czcum and vermi- 
form appendix being the most marked. 
If such is the case the early stages of development should give. 
indications of the previous primitive form. 
