Steriod-secreting cells exhibit unusual diversity in the cristae of their mitochrondria, like these examples from testicular Leydig cells of the ground squirrel Citellus lateralis. Small alveolar cristae are evident along the inner membrane; the double arrows in the upper panel highlight bundles of parallel tubules in the matrix, and single arrows (lower panel) show longitudinally oriented lamellar cristae. This image is courtesy of Jeffrey Pudney, and appears as Figure 248 in Chapter 7 (Mitochondria) of 'The Cell, 2nd Ed.' by Don W. Fawcett M.D. A PDF copy of the accompanying chapter is available on the ASCB’s BioEDUCATE website.