Sutra on Passing from One Existence to Another

Sutra on Passing from One Existence to Another 
Tibetan: 'Phags pa srid pa 'pho ba zhes bya ba'i mdo 
Sanskrit: Bhavasamkranti-sutra 
Kangyur vol. 35, no. 892. Lhasa Edition 227 Tsa 284a5-287a2.

The original Sanskrit texts of the Sutra on Passing from One Existence to Another and the Sutra on Death and the Transmigration of Souls are no longer extant and are known only through their Tibetan versions. Both Sutras deal principally with two topics, karma and its relation to rebirth. The popular and oft-quoted Sutra on Passing from One Existence to Another relates that during the Buddha's stay in Rajagriha, a certain king named Bimbisara questions him on the transitory nature of karma and how rebirth can be effected by thoughts and actions which are by their very nature momentary and fleeting. 

Sutra on Death and the Transmigration of Souls

Sutra on Death and the Transmigration of Souls
Tibetan: Tshe \316pho ba ji ltar \316gyur ba zhus pa\342i mdo 
Sanskrit: Ayupatti-yathakara-paripriccha-s!
Kangyur vol 39, no. 974. Lhasa Edition 311 La 223b7-237b3.

Characteristically, the Buddha responds with an illustration. In this context, an individual's past thoughts and actions (karma) appear before the mind at the time of death in the same way that the previous night's dreams are recalled while awake; neither the dreams nor past karma have any solid and substantial reality in themselves, but both can, and do, produce real effects. An individual's past karma appears before the mind at the final moment of death and causes the first moment of rebirth. This new life is nothing more than a new sphere of consciousness in one of the six realms of rebirth (the worlds of the gods, demi-gods, humans, hungry ghosts, animals, and hell- beings) wherein the person experiences the fruits of his or her previous  actions. From a Buddhist perspective, expressed for example in the Sutra on Death and the Transmigration of Souls, it is a mistake to refer to this specific cause and effect relationship as reincarnation since the Buddha explicitly denied the existence of a transmigrating soul that passes on from life to life. In reality, an entirely new consciousness arises at rebirth in dependence on the old. Continuity between lives is merely an illusion. 

Sutra on Entering into the Womb

Tibetan: Tshe dang ldan pa dga' bo mngal du 'jug pa bstan pa 
Sanskrit: Ayusman-nanda-garbhavakranti-nirdesa-sutra 
Kangyur vol. 23, no. 760. Lhasa Edition 58 Ga 380b5-399b2

Apart from its intriguing connections with the later death and intermediate state (bardo) literature of Tibet, the Sutra on Entering into the Womb is one of the most significant canonical sources for Tibetan medical literature devoted to the science of human reproduction and growth. In Tibetan medicine, human physical development is frequently explained as being analogous to the development of the universe. In this way, the ordinary dying and rebirth process is understood directly in terms of the ebb and flow of the cosmos. The Sutra on Entering into the Womb details the progression of a transmigrating consciousness from the final moment of death, to conception in the future mother's womb, and subsequently through each week of fetal development. In addition, this Sutra is perhaps the first to introduce the statement, repeated in the Tibetan Book of the Dead, that during conception the transmigrating consciousness, driven by an intense "oedipal" desire, will enter the womb and become male if it is attracted to its future mother and repulsed by its father, or female if attracted to its future father and repulsed by its mother. These intense, disruptive emotions of desire and hatred--which lie at the very heart of the ongoing cycle of rebirth--propel the consciousness into its new existence.