Actually as far as I know the Gospel of St. Thomas is considered to be part of the pseudopigrapha, not the apocrypha. Basically it is considered to be a later author writing under the name of Thomas (hence 'pseudo'=false in Greek, and 'grapha'=writings in Greek). It is not given the authority that an apocryphal writing would have. Do a search on the internet, you'll find the complete manuscript somewhere, it's not that long. From what I remember of it, it is a gnostic writing, in that it promotes a duality of spirit, body and mind.