THE PERCH 33 



A TELEOST FISH. THE PERCH 



The perch is one of the commonest fresh-water fishes. It is 

 found almost everywhere in streams, ponds, and lakes, where it 

 lives on small aquatic animals of every kind. Any other bony fish 

 may be used in place of the perch; the differences in structure 

 which exist will not confuse the dissection. Two or three speci- 

 mens will be needed for each student ; during the progress of the 

 dissection they should be kept in a 5 per cent solution of formalin 

 or in cold storage. For the study of the bones of the skull a larger 

 fish than the perch is a much more favorable object, and the cod 

 has been taken in its place ; the directions can, however, be used 

 also for the study of the skull of the perch. 



Observe the form and external markings of the animal. The 

 body of the perch, like that of the majority of teleosts, is elongated 

 and laterally compressed, with a wedge-shaped head and a ter- 

 minal mouth ; the hinder end is less compressed than the forward 

 portion and terminates with a homocercal caudal fin, which is the 

 principal organ of locomotion. The other fins are all of good size 

 and may be used both for purposes of locomotion and as a means 

 of defense against attack, the sharp spines with which most of 

 them are provided being formidable weapons. 



The entire body, with the exception of a part of the head and 

 the fins, is covered with ctenoid scales, which are not placed side 

 by side, as are the placoid scales of the dogfish, but overlap one 

 another posteriorly. Examine them carefully on different parts of 

 the body and note their arrangement and difference in size. If the 

 fish is fresh, note the slimy transparent epidermis which covers the 

 scales ; if it is not fresh, scrape off some of the dried epidermis. 

 Note the lateral line which runs along the entire length of the body 

 on each side, parallel with the back •, it is an organ of special sense. 



Observe the color bands and their arrangement. Are they bilat- 

 erally symmetrical? Note that the color consists of an aggrega- 

 tion of small dots, except where it forms solid masses. These dots 

 are pigment cells ; they are just beneath the epidermis in the outer 

 layer of the dermis and may be scraped off with the epidermis. 

 Note the structure of a single dot ; it will be seen to consist of a 



