1. Three species of flea were found on rats caught on the docks of Plymouth, England, namely, Nosopsyllus (Ceratophyllus) fasciatus, Xenopsylla cheopis, and Leptopsylla segnis (musculi).
2. The findings of Xenopsylla cheopis were almost entirely confined to a certain grain store, whence the flea was obtained constantly throughout the period of the investigation.
3. A few rats caught in the town of Plymouth yielded Leptopsylla segnis and Nosopsyllus fasciatus, but no Xenopsylla cheopis.