From iPhoto, you can easily access photos saved in your Aperture library.
To access your Aperture library:
Choose File > Show Aperture Library. (If you’re in full-screen view, move your pointer to the top of the screen to make the menu bar appear.)
The same view of your Aperture library organization that you see in Aperture appears on the left side of the window.
To move photos from your Aperture library to your iPhoto library, select the photos in your Aperture library and drag them into iPhoto.
The photos you dragged now exist in both applications, but they’re completely separate. If you edit the photos in iPhoto, those edits do not affect the copies in your Aperture library, and vice versa.
If you don’t see your Aperture library, open Aperture, choose Aperture > Preferences, and click Previews. In the “Share previews with iLife and iWork” pop-up menu, make sure you’ve chosen Always or “When quitting Aperture.”