About the skiagraphs, from website:
Skiagraphics of plants and shells are sometimes mistaken for delicate pen-and-ink drawings or for black-and-white photographs. When you look more closely, it becomes clear you’re not seeing a two-dimensional rendering of nature’s beauty, you are actually seeing through the leaves and petals and into the shells’ chambers. That’s because skiagraphics are X-ray prints of natural objects. The word skiagraphic comes from the Greek skia meaning shadow and graphic referring to drawing. An X-ray print is actually composed of overlapping shadows. Whereas a photograph is created when light bounces off a subject and onto light sensitive film, an X-ray is created when X-rays pass through an object and create shadows on X-ray-sensitive film. When a doctor flips an X-ray of your lungs onto a light box, he is looking at overlapping shadows.