In some episodes---Where is Everybody?,One for the Angels,Perchance to Dream,I Shot an Arrow Into the air,Mirror Image,and The Purple Testament---all good episodes---they used the traditional doo doo doo opening theme by Marius Constant,and for the closing music theme,the much softer closing theme by Bernard Herrmann.It's too bad that they didn't continue doing this in every episode,because the original closing theme by Bernard Herrmann was REALLY eerie.They ALSO used this -the traditional opening theme by Constamt and Herrmann's much softer closing theme- in these episodes -The Chaser,A Stop at Willoughby,and A World of His Own.

The original closing theme has always fascinated me. Soft, dark, profound, and devastating. I love Constant's classic theme as well but Hermann was able to produce something in his score that was beautiful and terrifying, something that captured the darkness and mystery of the series. The final few chords, especially, are just chilling and striking.

I may be wrong, but I think this theme was used throughout the entire first season and not just a select few episodes. Also I remember an abbreviated version of it plays during the opening credits as well of season 1. Constant didn't arrive until season 2.