CHAPTER III 
THE DISSECTION OF THE FISH 
E Blue-green Sunfish.—The organs found in the 
abdominal cavity of the fish may be readily traced 
in a rapid dissection. Any of the bony fishes may 
be chosen, but for our purposes the sunfish will serve 
as well as any. The names and location of the principal 
organs are shown in the accompanying figure, from Kellogg’s 
Zoology. It represents the blue-green sunfish, A pomotis cya- 
nellus, from the Kansas River, but in these regards all the 
species of sunfishes are alike. We may first glance at the dif- 
ferent organs as shown in the sequence of dissection, leaving a 
detailed account of each to the subsequent pages. 
The Viscera.—Opening the body cavity of the fish, as shown 
in the plate, we see below the back-bone a membranous sac 
closed and filled with air. This is the air-bladder, a rudiment 
of that structure which in higher vertebrates is developed as a 
lung. The alimentary canal passes through the abdominal cavity 
extending from the mouth through the pharynx and ending at 
the anus or vent. The stomach has the form of a blind sac, and 
at its termination are a number of tubular sacs, the pyloric 
czeca, which secrete a digestive fluid. Beyond the pylorus ex- 
tends the intestine with one or two loops to the anus. Con- 
nected with the intestine anteriorly is the large red mass of the 
liver, with its gall-bladder, which serves as a reservoir for bile, 
the fluid the liver secretes. Farther back is another red glandu- 
lar mass, the spleen. 
In front of the liver and separated from it by a membrane 
is the heart. This is of four parts. The posterior part is a 
thin-walled reservoir, the sinus venosus, into which blood 
enters through the jugular vein from the head and through 
the cardinal vein from the kidney. From the sinus venosus 
it passes forward into a large thin-walled chamber, the auricle, 
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