Board Thread:Questions and Answers/@comment-5991191-20151127025059/@comment-18812574-20151127053334

First of all, it's "their" not "there". Secondly, check the definition for a Menos:

Menos are conglomerations of hundreds of normal Hollows, resulting in a single composite entity of far greater strength than any normal Hollow.[20]

To evolve from Hollow to Menos the Hollow must be too powerful to subsist on Human Souls alone. And to evolve from a Menos Grande to an Adjuchas the Menos Grande must differentiate themselves and continue to eat other Menos. The way they differentiate themselvs is that, in that huge, mushed together pile of Hollows one soul in particular gains control over the rest. While it is possible that the one dominant personality that emerges from this mass of souls may retain his/her memories, I think it might be highly unlikely to say they retain memories of their past lives once they begin to evolve. The only exception I can think of is Aaronierro, who retained Kaien's memories. But that obviously was a very, very special case.