storage - Where does Google Play store its ebooks on an Android device?

In the Google Play Books Android application, there is an option to keep an ebook on a device if the user wants to do it. So when you decide to do such a thing, the ebook may be stored somewhere on the Android device. I would like to know where the ebook is stored. I searched in /mnt/storage and I only found Aldiko ebooks (in the /mnt/storage/eBooks folder), not the Google Play eBooks.

Thanks for your answsers.

PS : if it can help, I do this on an Archos G9 101 tablet.