Figure 1.

Monitoring of the guinea pig vaginal membrane. During the latent period of the estrus cycle, the guinea pig vaginal membrane (dashed outline) is visibly closed (A,B). Four to five days prior to ovulation, changes to the color of the vaginal membrane can be observed indicating potential membrane perforation (C). At the time of ovulation, the vaginal membrane perforates and increased vaginal secretions/mucus can be observed (D). Following ovulation, the vaginal membrane begins to close (E,F). The closed arrow indicates the urethral opening, the open arrow indicates the anus.