The Form of the Penis in the British Rhinolophid Bats, compared with that in some of the Vespertilionid Bats; and (2) The Female Sexual Cycle in the British Horse‐shoe Bats, Rhinolophus ferrum‐equinum insulanus Barrett‐Hamilton and R. hipposideros minutus Montagu.

Summary. 1. Although the penis of the Chiroptera is generally described as pendulous, it is directed cranially in Rhinolophus ferrum‐equinum insulanus and R. hipposideros minutus. 2. In five species of British Vespertilionid bats the penis varies from the cranially directed type to the completely pendulous type. 3. The glans penis in the Rhinolophidse is large and complicated in architecture, but in the Vespertilionidse it is very small and comparatively simple. 4. The form and structure of the glans penis and prepuce in R. ferrum‐equinum insulanus and R. hipposideros minutus are briefly described and compared with those of five species of British Vespertilionid bats. 5. The biological correlations and taxonomic importance of the differences in the form and structure of the glans penis in the Rhinolophidae and the Vespertilionidae are indicated.