194 THE ANIMALS AND MAN 



It loses its tail and with it the short notochord possessed by 

 the larva; the eye and the auditory organ are lost, and the 

 nervous system and alimentary canal become much reduced 

 and simplified. Sea-squirts in their adult stage are very 

 simple degenerate animals, with low functional development, 

 yet their embryonic and larval conditions show a consider- 

 able degree of structural specialization, and the presence of 

 the notochord in these early stages reveals their affinity with 

 the backboned animals. 



The fishes. — We have already studied (Chapter II) an 

 example of the class of fishes. The sunfish is common in 

 streams and ponds all over the country, and its habits can 

 be well observed by patient students. It lives in quiet 

 corners of brooks and rivers, preferably under a log or at the 

 root of an old stump. It is a beautiful fish, shining "like a 

 coin fresh from the mint." Its body is mottled golden, 

 orange, and blue, with metallic luster, darker above, pale or 

 yellowish below. Its fins are of the same color. The tip 

 of its opercle or gill-cover is prolonged like an ear, and jet 

 black in color, with a dash of bright scarlet along its lower 

 edge. Nearly all of the thirty species of sunfish found in the 

 United States have this black ear-like opercle, but some 

 have it long, some short, and in some it is trimmed with 

 yellow or blue instead of scarlet. 



The sunfish lays its eggs in the spring in a rude nest 

 scooped out in the gravel over which the male stands guard 

 with its bright fins spread, looking as big and dangerous 

 as possible. When thus.employed it takes the hook savagely, 

 perhaps regarding the worm as a dangerous enemy. The 

 young fishes soon hatch, looking very much like their parents, 

 although more transparent and not so brightly colored. 

 They grow rapidly, feeding on insects and other small 

 creatures, and reach their growth in two or three years. 

 They do not wander far and never willingly migrate. Stu- 

 dents should verify this account on the different species. A 



