1.we (主句主语)
2.have only to turn to (谓语部分)
3.that extraordinary discovery of echo-location in bats to see a case in which the voice plays a strictly utilitarian role(宾语部分)
4.in which the voice plays a strictly utilitarian role(宾语从句中的一个定语从句修饰case)
(we) have only to ((turn to)) (((that extraordinary discovery of echo-location in bats)))
we turn to that。。。。的目的是to see a case
什么样的case??即the voice plays a strictly utilitarian role