ALIMENTARY TRACT OF THE KING SALMON 
87 
salmon the average length for the first limb is from 9 to 10 cm., that of the second limb 
from 28 to 30 cm. The last 4 or 5 centimeters of the intestine form a somewhat prom- 
inent enlargement, the cloaca. 
There is a considerable variation in the size of the intestinal tube, even in fishes 
of the same length. This variation is greatest in the pyloric portion where the numer- 
ous caeca are attached. The variation in size is, however, dependent upon the degree 
of distension by food materials. It is largely an adaptation of the tube to its content, 
in so far as the diameter is concerned. If the tube be widely dilated the structural walls 
are correspondingly thin. 
APPENDAGES OF THE INTESTINE. 
Along the full length of the pyloric intestine there are numerous diverticula, the 
pyloric caeca. There is considerable variation in the number of caeca in different indi- 
viduals of the genus Oncorhynchus. Jordan and Evermann, in “Fishes of North and 
Middle America,” state that the number of caeca in the king salmon varies from 140 
to 185. The larger number would seem to be more nearly the average. 
The caeca are absent from the line of the wall of the pyloric intestine represented 
by the inner curvature. This line is marked by the attachment of intestinal blood 
vessels and of the gall and pancreatic ducts. All other portions of the wall of this 
limb of the intestine are studded thickly with pyloric caeca. The caeca, as a rule, arise 
as individual diverticula coming off at right angles to the surface and then bending 
posteriorly to lie like a fringe about the end of the pyloric stomach, and overlapping 
each other from this point for the full extent of the pyloric intestine. (See fig. i.) 
The diameter of a caecum at the base is usually somewhat less than in the main body 
of the diverticulum, averaging from 5 to 6 mm. Just outside the bases the caeca are 
somewhat larger — ^from 7 to 8 mm. in diameter. From this point to their tips they 
taper very gently to terminate in a blind sac. 
The lengths of the caeca vary greatly in different regions of the pyloric intestine. 
The longest caeca are found at the origin of the intestine and just within the pyloric 
valve. At this point the appendages reach a length of from 6 to 8 cm., even longer 
in larger fishes. In any given segment those caeca that border on the line of the inner 
curvature are apt to be slightly shorter than the others in this segment. The lengths 
diminish progressively from the pyloric valve to the most anterior portion of the pyloric 
intestine. The last caeca are found on the ventral surface of the dorsal portion of the 
pyloric intestine, just where the anterior bend ceases and the straight limb of the 
intestine begins. These caeca are often i cm. or less in length, and the last two or three 
usually stand in a single row along the extent of the intestinal tube. 
The pyloric caeca in their number, size, and arrangement form one of the most 
striking characteristics of the intestinal tract of this entire genus. In fact, the number 
is sufficiently constant to be given by systematists as a specific character. In the 
past the physiological function of these organs has been somewhat in doubt, but in 
the course of this work we have, fortunately, been able experimentally to establish 
certain points in their physiological economy to the salmon. 
