How does socket select() work?

As described in network programming books, select() monitors a set of file descriptors for reading. For example, here is part of code:

select(numfds, &read_fds, NULL, NULL, NULL);

Here numfds is maximum number of socket in read_fds + 1. Does it mean, that every "monitor" cycle select() watchs through all file descriptors of the process from 0 to numfds? I mean, if I have only two file descriptors to monitor(0 and 26), does select watch all descriptors from 0 to 26?