Depends on how you import them.
There are two ways Aperture will handle the original files, the first called managed is when the original is copied into the Aperture library itself, the second called referenced is where the originals are kept outside the library.
Which system is used depends on what settings you have in Aperture when you import the originals. The default is managed so if you did not change anything then most likely the originals are in the library.
You can tell by selecting the Photos icon in the library view of the Inspector, switch to Browser view, selecting all the images in the library and doing a File->Locate Referenced Files.
If any images are shown in the window that opens those are referenced.