Method of Preparation.

The flea is soaked for a week or so in a caustic potash solution, which dissolves the internal organs. After neutralization in acetic acid, it is pressed flat between two microscope slides, and dehydrated by immersion in ethanol solutions of increasing strength. At this stage, no trace remains of the internal organs. After a final clearing in clove oil, the now flat and brittle exoskeleton is mounted under a coverglass in Canada balsam.