aquatic ILitt 



37 



by two kinds of tin-rays ; the spinous por- 

 tions by hard, unsegmented and un- 

 branched rays or spines ; the other by 

 soft, segmented and branched rays. The 

 other fins are of the branched form. The 

 caudal fin or tail is the one generally 

 used for propulsion. A movement of the 

 caudal to the right will bring the fish 

 forward and to the left, a movement to 

 the left brings it forward and to the 

 right ; by means of two strokes in quick 

 succession, one to the right and one to 

 the left, the side motion is counteracted 

 and the fish moves forward in a straight 

 line. The other fins are generally used 

 in steering and in maintaining an equi- 

 librium. Along the side of the body, gen- 

 erally half way between the dorsal and 

 ventral surfaces, is what is called the 

 lateral line. Along this line the scales 

 are somewhat modified, and beneath them 

 are situated sense organs that respond to 

 very low frequency vibrations, it being 

 supposed that these organs stand between 

 those of true hearing and those of touch. 

 Protective coloration, which nearly all 

 fishes possess in greater or less degree, is 

 fairly well developed in the perch. The 

 dorsal surface is of a rather dark shade 

 to correspond with the dark bottom of 

 most lakes and streams when the fish is 

 viewed from above. The ventral surface 

 is of a very light color to correspond with 

 the light of the surface when the fish is 

 viewed from below. And lastly the sides 

 are more or less mottled, which makes 

 the fish much less conspicuous in his 

 surroundings of vari-colored roots, 

 plants and rocks. The mouth consists of 

 two portions; the lower moveable jaw 

 or mandible (6) and the stationary upper 

 jaw or maxilla (7). On the snout, a 

 short distance above the mouth, are situ- 

 ated two small projections, which are the 

 nostrils (8). They are peculiar in the 

 fishes, as contrasted with other animals, 



in that they are not connected with the 

 respiratory apparatus. The eyes are 

 moveable, but have no eyelids. Behind 

 the eye, on each side of the head, is situ- 

 ated an opercle or gill covering. These 

 opercles protect the delicate gills, and if 

 necessary may be clamped down with 

 surprising strength. 



It has been said that there are only 

 two things worth while to a perch, and 

 these are "To eat and not to be eaten." 

 We have already seen how the perch 

 avoids being eaten by his powers of loco- 

 motion and somewhat protective colora- 

 tion. We will now see how he eats. 



Most fish have teeth, the most primi- 

 tive of which are small papilla? or rough 

 elevated spots. The two kinds most gen- 

 erally found, however, are more pro- 

 nounced in form and are the moveable 

 teeth and the firm or fixed teeth. They 

 may be situated on the lower jaw or man- 

 dible only or on both the mandible and 

 maxilla or upper jaw, depending upon 

 the species. The moveable teeth are 

 merely imbedded in the skin of the 

 mouth, and generally indicate that the 

 fish possessing them subsists mainly on 

 a herbivorous diet. The fixed teeth are 

 larger and stronger than the moveable 

 ones, and are firmly set in the bone be- 

 neath the skin. This form is generally 

 possessed by the carnivorous fishes, and 

 helps them in holding fast their prey. 

 In some fish a few of the teeth in the 

 front of the mouth are enlarged and are 

 called incisors, being used for cracking 

 snail and crab shells. In the sharks the 

 teeth are being continually formed on the 

 inner margins of the jaw and the old 

 ones pushed out over the edge. On the 

 ventral surface of the mouth is a fleshy, 

 generally immoveable tongue ( 10), which 

 varies in size in the different genera. 

 Back of the tongue is the pharynx, with 

 S;ill slits on both sides, which allow the 



