Q: How do I retrieve Photobooks created in Aperture, from Photos after upgrade to Yosemite?

I have been creating photobooks for printing, using Aperture.

Recently I upgraded to Yosemite, and realised I can't find the photobooks in Photos. The albums are still intact though.

May I know if the photobooks created are imported into Photos, and if yes, how do I retrieve them?

Thanks.