FISHES 209 



passes over the outside layer, or cornea of each eye. The 

 pupil is large and conspicuous, and each eye is surrounded 

 by a circular fold of skin and set in a protective socket. 



Mouth and nostrils. — The perch can open the upper 

 and lower jaws so wide that the mouth appears as a circular 

 aperture almost as large as the circumference of the body. 

 The perch lives upon smaller fish, worms, insects, etc., 

 which are caught alive in its capacious mouth. Tlie mouth 

 is fiu-nished with numerous small teeth that are present, 



Dorset! Jlns 



Caudal 

 fill 



m}m Altai jiih 



Pelvicfin 



Fig. 146. — Diagram of a perch. 



not only on both jaws, but on the roof of the mouth and roof 

 and floor of the pharynx. The teeth are not strong enough 

 to masticate the food to any extent, but are suitetl to hold 

 the prey of the perch. 



In front of each eye, on the head, are two openings, the 

 nasal apertures, or nostrils. These do not commimicate 

 with the mouth as in the mannnals, but lead to a pair of 

 sacs, the 7iasal sacs, situated withui the head above the roof 

 of the mouth. 



Fins. — The perch has eight fins of which four are borne 

 in pairs, therefore known as the faired fins. The remaining 



herrick's zool. — 14 



