Not all sounds made by animals serve as language, and we have only to turn to that extraordinary discovery of echo-location in bats to see a case in which the voice plays a strictly utilitarian role.
To get a full appreciation of what this means we must turn first to some recent human inventions.
为了充分理解这一点，我们必须先看看人类最近的一些发明。
Everyone knows that if he shouts in the vicinity of a wall or a mountainside, an echo will come back.
每个人都知道，如果在墙壁或山坡附近大声喊叫，就会有回声。
The further off this solid obstruction, the longer time will elapse for the return of the echo.
离坚固的障碍物越远，回声返回的时间就越长。
A sound made by tapping on the hull of a ship will be reflected from the sea bottom, and by measuring the time interval between the taps and the receipt of the echoes, the depth of the sea at that point can be calculated.
So was born the echo-sounding apparatus, now in general use in ships.
回声探测仪就这样诞生了，现在已在船上普遍使用。
Every solid object will reflect a sound, varying according to the size and nature of the object.
每个固体物体都会反射声音，声音的大小和性质各不相同。
A shoal of fish will do this.
一群鱼就会这样。
So it is a comparatively simple step from locating the sea bottom to locating a shoal of fish.
因此，从确定海底位置到确定鱼群位置是一个相对简单的步骤。
With experience, and with improved apparatus, it is now possible not only to locate a shoal but to tell if it is herring, cod, or other well-known fish, by the pattern of its echo.
It has been found that certain bats emit squeaks and by receiving the echoes, they can locate and steer clear of obstacles -- or locate flying insects on which they feed.
