212 BRANCH CHORDATA 



present. The swim-bladder is usually present, but its duct is 

 often closed. Eyes are usually conspicuous and without lids. 



Reproduction is by eggs. They are small and numerous, 

 and are fertilized in the water by the milt deposited by 

 the male at the same time. This accounts for the enormous 

 schools of some fishes in certain places at the breeding season 

 each year. They sometimes go thousands of miles to reach these 

 spawning places. The salmon come from the salt water up 

 into the rivers to deposit their eggs, which are about the size 

 of peas, in depressions or nests. When very small the young 

 salmon are banded and called parr, and later become silvery 

 smolt. The perches form nests or hollows in the ground near 

 the shore. In a form allied to the perch both male and 

 female form these depressions and guard the eggs. The male 

 Chromis of Lake Tiberias carries the eggs and young in its 

 mouth. The stickleback (see Fig. 163), a small fresh-water 

 fish, builds a nest and the male cares for the young. The 

 male Loph'obranch carries the eggs in a ventral pouch, forcing 

 the young out by pressing the pouch against a stone. An 

 Indian ocean form carries the eggs in a pouch formed by the 

 ventral fins of the mother. 



Sub-order Physos'tomi includes the catfishes, buffalo, carp, 

 salmon, trout, herring, eels, etc. 



The catfishes (Silu'ridas) are devoid of scales. The majority live in 

 fresh water. The head is flat and the wide mouth is provided with long 

 thread-like feelers or barbels. They have, for a weapon of defense, a strong 

 stiff spine for the first ray of dorsal and pectoral fins. They are sluggish 

 and abound in the muddy streams of the Mississippi Valley. The flesh is 

 quite free from bones and is much used for food. Some catfishes weigh 

 150 pounds. 



The common catfish guards its young. The South American catfish 

 carries its eggs and young in its mouth. Other South American species 

 build nests of leaves in which they place their young. An electric catfish 

 inhabits the Nile, and blind catfishes live in subterranean streams of Penn- 

 sylvania. 



Carps, buffalo fishes, and suckers have a naked head and usually scaly 

 body. The flesh is bony and not of much food value, yet quite largely used 

 because inexpensive on account of the immense number seined. They have 

 a toothless sucking mouth and are vegetable feeders, hence the intestine 

 is long. The air-bladder consists of two or three links. . . . The 

 shiners, minnows, and dace (Fig. 175) belong to this group. The black- 

 nosed dace (Rh'inich'thys atronasus) is a nest builder. Both male and 

 female form a depression in which the eggs are deposited. Both parents 



