Spider-Man theme song, are the singers women or both men and women?

I am referring of course, to the original Spider-Man theme song, 1967 version. The voices are so confusing, they SEEM to sound like female or female mostly, but the sound of them is quite strange, sometimes it sounds like men pretending to sing like women, or like women and men singing together.

I checked on Wikipedia and what I found there was useless to me, it explains about the composers, but not about the singers themselves.

Any help to solve this puzzle will be greatly appreciated!