INTRODUCTION, 



ANATOMY. 



Since this report is to be brief and preliminary only those points 

 concerning the anatomy used in determining the systematic posi- 

 tion of the different fishes will be considered. To arrive at these 

 points it will be well to study the common perch {Perca flavescens), 

 which abounds in all the waters of Minnesota. Besides being a 

 famUiar flsh, the perch represents a type with which we can com- 

 pare the anatomy of all our other fishes. 



The fins on the back are called the dorsal. In the perch there 

 are two, a front or anterior one called the spinous dorsal, and a back 

 or posterior one called the soft dorsal. The spinous dorsal possesses 

 stiff, sharp spines called rays, while the soft dorsal possesses many- 

 jointed very flexible rays that do not end in hard, sharp points. 

 These fins may be near each other, as is the case with the perch; 

 they may be widely separated, or there may be but one and that a 

 soft dorsal, like the posterior dorsal fin of the perch. In some fishes, 

 cat-fish, white-fish and others, the posterior dorsal is simply a fatty 

 lobe, and it is then called the adipose fin. In a few of the cat-fishes 

 this adipose fin is continuous with the tail or caudal fin. 



The caudal fin may be entire, said of it when the posterior edge 

 is about even, or forked, when the posterior edge is notched. When 

 the two lobes of the caudal are of about the same size it is said to be 

 homoceroal, but when the upper lobe is larger and longer than the 

 lower lobe and has in it the continuation of the spinal column, the 

 caudal fin is said to be heterocercal, illustrated in the sturgeon. 



The fin on the lower or ventral side of the body nearest the 

 caudal is the anal. It may be made up of soft rays entirely or of 

 both spines and soft rays, as it is in the perch. Its length, kind 

 and number of rays are often essential in identification. 



The two fins just in front of the anal are the ventrals. These 

 may be placed far forward, as they are in the perch, when they are 

 said to be thoracic or jugular or they may be near the middle of the 

 belly, as in the suckers, when they are said to be abdominal. 



The remaining fins are the pectorals. These may vary some- 

 what in size and location, but otherwise are about constant. When 



