312 GENERAL ZOOLOGY 



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. These organs are sensi- 

 tive to mechanical jars of a low rate of frequency, thus stand- 

 ing between organs of touch proper and those of hearing. 



Fig. 159. Yellow perch 1 



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 oper- 

 culum, 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 



iFrom The Fishes of Illinois, by S. A. Forbes and R. E. Richardson. 



