they can locate and steer clear of obstacles -- or locate flying insects on which they feed.

并能通过回声来确定并躲开障碍物，或找到它们赖以为生的昆虫。

and beyond six or seven they are worthless.

如果超过六七天，天气预报就没有了任何价值。

And although no period or place in American history has been more absurdly romanticized, myth and reality did join hands in at least one arena, the conflict between the individual and encroaching civilization.

虽然在美国历史上没有任何时期或地区像西部拓荒时期那样被荒谬地浪漫主义化了，但神话和事实至少在某一个舞台上共存，也就是存在于个人与渐渐闯入的文明这两者的冲突之中。

But even in the most favourable circumstances only a small fraction of the creatures that die are preserved in this way before decay sets in or, even more likely, before scavengers eat them.

即使是在最有利的环境中，死去的生物中也只有一小部分能在开始腐烂前，或更可能在被食腐动物吃掉之前，被这样保存下来。

and its owner his or her full intelligence;

和智力还有待发展和完善，

from the search for what his world contains at its inmost point.

脱离了对自己灵魂最深处世界的探索。