306 GENERAL ZOOLOGY 



along the Atlantic coast, and westward in the region of the 

 Great Lakes and upper Mississippi valley. Though origi- 

 nally absent from the far West, it has recently been intro-- 

 duced with success into the lakes of Washington, Oregon, 

 and California. In structure and habits our yellow perch 

 very closely resembles the perch of Europe, referred to in the 

 quotation at the head of this chapter, and by some authors 

 it is considered to be identical with the latter species. 



External Structure. The body of the perch is elongate, 

 slightly compressed from side to side, and tapers toward both 

 ends. Three divisions are apparent, the head, trunk, and tail; 

 several appendages, the fins, are attached to the body. The 

 covering is a smooth skin, containing pigment cells, to which 

 the colors are due, and glands which secrete mucus. Within 

 pouches in this skin are transparent scales, which overlap, 

 like the shingles on the roof of a house, and form a coat of 

 mail, incasing the fish from head to tail. Along a clearly 

 defined lateral line the scales are somewhat modified, and 

 beneath them are sense-organs the functions of which have 

 been variously stated. Professor G. H. Parker considers that 

 these organs are sensitive to mechanical jars of a low rate of 

 frequency, thus standing between organs of touch proper, and 

 those of hearing. 



At the anterior end of the head are the jaws, armed with 

 teeth for seizing food. The eyes have no eyelids. Just in 

 front of the eyes are the nostrils, two on either side. They 

 have no communication with the mouth. Behind the eyes, on 

 each side of the body, is a movable flap called the operculum, 

 beneath which are the red comb-like gills.. 



There are five fins, three unpaired and two in pairs. Of the 

 unpaired fins those on the back are called the dorsal fins, the 

 one on the under side the anal fin, and the one at the tail 

 the caudal fin. The more anterior of the paired fins are the 

 pectoral fins ; the more posterior and lower, the ventral or 



