Other lists were evidently issued later, as slides with numbers as high as 250 are known.
The slides were evidently mass produced by anonymous preparers.Stevens’ support in selling those items was critical to the successes of exploring and collecting expeditions, as he would send profits from the sales back to the collectors, allowing them to stay in the field for years on end.Stevens charged a 20 percent commission on those sales, plus an additional 5 percent for insurance and freight.An example of a going retail price was 4 pence per insect, which would return 3 pence to the collector.Stevens wrote his 1855 Directions for Collecting and Preserving Specimens of Natural History in Tropical Climates in large part to assist those explorer-collectors.The slide numbered 67 is a section from the wing of the butterfly Morpho menelaus, a species from South America.
It is highly probable that this butterfly wing was sent to Stevens by Bates or Wallace.
Examples of Samuel Stevens’ support of explorer-collectors.   The two most famous explorer-collectors supported by Stevens were Alfred Russel Wallace and Henry Bates, both of whom played significant roles in the early development of evolutionary theory.
Wallace wrote influential works on evolution, and his ideas spurred Charles Darwin to publish his own work.
These numbers were part of an efficient selling scheme, by which customers could chose the specimens they preferred from a printed list, then order their selections using the corresponding number (Figure 2).
It was much like the menu system used in many restaurants today.
A competitor, James Tennant, sold microscope slides with labels that were virtually identical to those of Stevens and used a similar numbered list sytem. Six slides from Samuel Stevens’ Natural History Agency, dating between 18.