The cortex (the first two slides) can be identified by the distinctive rounded corpuscles (3) with grape-like clusters of glomeruli (2) inside.
The medulla (last slide) contains only a dense arrangement of tubules. The medulla lacks corpuscles.
The round structures are renal corpuscles (3), consisting of an outer Bowman's Capsule (1) and the glomerulus (2) inside.
Most of the other structures visible in these photographs are proximal and distal convoluted tubules.