rather than as organs of hearing. Fishes from which these internal ears have been removed are unable to maintain their equilibrium.

Some fishes have special organs that serve as tactile organs such as are found on the under side of the head of a cod (Fig. 108) and also on the head of bullheads (Fig. 101). Along each side of the body and tail of fishes is a series of little openings or pores which form what is known as the lateral line (Fig. 108). These organs are supposed to he principally organs of touch.

104. Reproduction and life history. The flowers of seed plants are devoted to the production of seeds which, in turn, produce new plants of the same kind (P. B., 83). Likewise in fishes there are special organs the sole function of which is the production of new individuals. The organs of fishes which may be said to correspond in function to the stamens and pistils of flowers are the ovaries (Fig. 98) and spermaries. In the ovaries are produced many egg-cells, and the mass of eggs in the ovary of a fish is often called the roe. In order that an egg may develop it must first be fertilized by a sperm-cell from the spermary of a male fish. This process usually occurs in the water after the ripe eggs and sperm-cells have been extruded from the ovaries and spermaries of the parent fishes.

You will recall the fact that the pollen tube containing a sperm-nucleus makes its way into an ovule and that the

sperm-nucleus is forced into the ovule and unites with the egg-nucleus; this is the process known as fertilization (P. B., 91). In the case of fishes the sperm-cells swim to the eggs, and then force their way into the egg (Fig. 102, A).

The nucleus of the sperm- and egg-cells then unite just as in plants (Fig. 102, B, C, D). first divides, and then the two cells. Each of these four cells are produced (Fig. 103, A, B). The process of

The egg nucleus thus fertilized cell body, and thus are formed cells in turn divides, and so

division continues until a many-celled organism is developed.

As the cells increase in number, they become different in character and form the various organs of the body. When the little fish first hatches, and begins to swim about, it often has attached to it some of the food substance (yolk) stored in the egg (Fig. 103, D). After this is used up, the young fish must secure its own food.

Most fishes do not take any care of their eggs or young, and in some cases the parents die soon after the eggs are laid and fertilized. In the case of the stickleback, however, the male fish makes a nest (Fig. 104) in which the females deposit their eggs. The male then extrudes sperm over the eggs. The male stays about the nest and guards the eggs and also

FIG. 105. Artificial fertilization of eggs. (Coleman.)

the young sticklebacks when they hatch out.

105. Artificial propagation of fishes. Since, as we have said, most kinds of fishes give no attention to eggs or young, enormous numbers of both eggs and young are eaten by other fishes; hence, only a small proportion come to maturity. For example,

while a codfish lays 8,000,000 eggs, only about two of these eggs on the average come to maturity. Hence, in order to increase to any considerable extent the number of fishes, the eggs are artificially hatched. That is, the fish

are caught when the eggs are ripe and the eggs are gently squeezed from the ovaries into the water (Fig. 105). Then some of the sperm-cells are similarly squeezed from the male fish and mixed with the eggs. This provides for fertilizing most of the eggs, which would probably not occur in nature. Special apparatus is devised for keeping the eggs supplied with fresh water until they hatch (Fig. 106). When the

young are old enough they are fed for a time, then the young fry, are set free in the waters where more fish are desired. Millions of young fish are every year distributed by the government all over the United States to be placed in ponds, rivers, and lakes where the supply is deficient, or in the ocean. along the shore.

106. Economic importance of fishes. times fishes have formed a considerable peoples that lived near bodies of water.

From very ancient part of the food of The importance to