166 ANIMAL FORMS 
seaweed, the male carrying the eggs about in his pocket 
until they hatch; the mullet, stupid, blundering, feeding 
on minute plants, crushing them in a gizzard like that of 
a hen, but withal having soft flesh, good for the table; the 
flying-fishes, which sail through the air with great swiftness 
to escape their enemies. 
161. The spiny-rayed fishes—In the group of spiny- 
rayed fishes the ventral fins are brought forward and joined 
to the shoulder-girdle. The scales are generally rough to 
the touch, and the head is usually roughened also. There 
are many in every sea, ranging in size from the Everglade 
perch of Florida, an inch long, to the swordfish, which is 
thirty. These are the most specialized, the most fish-like 
of all the fishes. Leading families are the perch, in the 
fresh waters, the common yellow perch, familiar to all boys 
in the Northeastern States; the darters, which are dwarf 
perches, beautifully colored and gracefully formed, living 
on the bottoms of swift rivers; the sunfishes, with broad 
bodies and shining scales, thriving and nest-building in 
the quiet eddies; the sea-bass of many kinds, all valued for 
the table; the «mackerel tribe, mostly swimming in great. 
schools from shore to shore. After these come the multi- 
tude of snappers, grunts, weakfishes, bluefishes, rose-fishes, 
valued as food. Then follow the gurnards, with bony 
heads; the sculpins, with heads armed with thorns, the 
small ones in the rivers most destructive to the eggs of 
trout; and at the end of the long series a few families in 
which the spines once developed are lost again, and the 
fins have only soft and jointed rays. It is a curious law of 
development that when a structure is once highly special- 
ized it may lose its usefulness, at which point degeneration 
at once sets in. Among fishes of this type are the cod- 
fishes, with spindle-shaped bodies, and the flounders, with 
flat bodies. The flounders lie on the sand with one side 
down, and the head is so twisted that the eyes come out to- 
gether on the side that lies uppermost. This side is col- 
