What does Jerry's swim through the tunnel symbolize in "Through the Tunnel"?

Jerry's swim through the tunnel symbolizes a rite of passage from boyhood to young manhood.

A coming-of-age story, Doris Lessing's "Through the Tunnel" uses symbols to represent Jerry's state of being and his rite of passage. The tunnel of the large rock under the water out in the "wild bay" symbolically represents this rite because swimming through this long passage requires manly discipline and stamina.

Certainly, an examination of Jerry's behavior when he first witnesses the older boys' feat of diving into the dark water and emerging some time later indicates his immaturity. For instance, after plunging down a few times in search of the opening, Jerry sees the other boys preparing to dive again:

And now, in a panic of failure, he yelled up, in English, "Look at me! Look!" and he began splashing and kicking in the water like a foolish dog.

Jerry's childish clowning receives only disdain from the older boys, and his failures to compete with them causes them to swim back to shore without even looking at him. Once on shore they gather their clothes quickly and run to another promontory. Feeling their rejection, Jerry immaturely "cried openly, fists in his eyes."

But, after he swims to shore and returns to the villa and his mother, Jerry demands that she purchase swim goggles for him as he has resolved that he will discover the opening to the tunnel and train himself to make the passage. After days of increasing his lung power, Jerry is finally able hold his breath long enough to swim through the hole that he has succeeded in discovering. When he emerges from the tunnel, Jerry "wanted nothing but to get back home and lie down," even though he sees the older boys some distance away. "[I]t was no longer of the least importance to go to the bay" because Jerry has proven himself the equal of the older boys; he has accomplished his rite of passage.