From left to right: Bicellaria grandis, section of cow's hoof, long section of fossilized coral, water scorpion (Nepa cinerea)
19th-century naturalists packaged specimen slides — cross-sections or small, whole organisms pressed between glass slides — in much the same way they packaged everything else: ornamentally.
As microscopes and lenses became more sophisticated, and glass slides gained popularity in Victorian England, commercial glass slide mounters began to emerge in order to meet the demand of amateur naturalists. Many of the commercial slide makers began attaching decorative lithographed wrappers to the glass, often fixed with small handwritten identification tags and monogrammed trademark labels. Individual slide mounter's work became very recognizable over time, and have retained considerable value when found in near original condition.
These examples above, taken from A Cabinet of Curiosities, are just a tiny example of the wide array of surviving pieces. Letterology has a great brief history and more images, or you can check out the full catalogue if you have a few hours to get lost in the Internet. Link