It is well known that through the consecration (diksa) of the Agnistoma, a basic type of Soma sacrifice, the sacrificer simulates an embryo (garbha) to be reborn as one of the gods. This is based on the assumption that prior to the diksa, he meets with ceremonial ‘death’.
But it has not been considered in detail how and when the sacrificer ‘dies’. In this paper, I analyze the Yajur-Veda's brahmana portions of the diksa, especially the diksaniyesti.
I have found the following: The Maitrayani-Samhita and the Kathaka-Samhita, which are regarded as the oldest among the brahmanas, clearly indicate that a cake or rice gruel, the offering for this isti, is a symbol of the sacrificer, and he is ‘killed’ symbolically as a victim. On the other hand, these are merely implied in the Taittiriya-Samhitd and the Satapatha-Brahmana which are considered relatively new.
It seems that this idea seen in the MS and the KS has been adjusted under the notion of identifying an offering with the sacrificer in the new and full moon sacrifice, which is a basic type of isti.
The relation between the diksa and the animal offering is noteworthy. It is also well known that the consecrated sacrificer regarded as an offering has to redeem himself by offering an animal sacrifice, namely agnisomiyapasu. So he is supposed to ‘die’ prior to the animal offering, and it is in this very isti that he is symbolically ‘killed’ as a victim.