198 PHYLUM CHORDATA 



Class : Pisces. Order : Teleostei 

 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, but a partial dissection 

 can be performed with a single specimen. During the progress of 

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

 formalin or in cold storage. 



Observe the form and external markings of the animal. The 

 body of the perch, like that of the majority of teleosts, is elon- 

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

 a terminal mouth ; the hinder end is less compressed than the 

 forward portion and terminates with the tail 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 scales, which overlap one another poste- 

 riorly. 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 each side of the body 

 parallel with the back its entire length ; it is an organ of special 

 sense, being sensitive to vibrations in the water. 



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

 laterally symmetrical ? Note that the color consists of an aggre- 

 gation 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 



