CHAPTER III 

 THE DISSECTION OF THE FISH 



[he 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 

 Zoologv. It represents the blue-green sunfish, Apomotis cya- 

 nclliis, from the Kansas River, but in these regards all the 

 species of sunfishes are alike. ^A^e 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 

 CEeca, which secrete a digestive fluid. Bej^ond 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. 



26 



