Figure 3.

Flow diagram used for classifying digital images of the uterus and vagina of mated females into one of 10 stages of sperm storage. Images were first classified as either “Contracted (curved)” or “Open (straight)”. “Contracted” and “curved” refer to the general conformation of the lower reproductive tract (i.e. as seen in Stages 1–4). In these early stages, substantial contraction of the circular and longitudinal muscles surrounding the uterus occurs, causing folding of the uterus and minimizing the available space within the uterus lumen. The term “Open” refers to the fact that, by Stage 5, the uterus lumen has opened into a single contiguous space. In the latter stages of sperm storage (5–10), the uterus is “straight,” indicating that a straight line can be drawn from the seminal receptacle, through the uterus lumen, to the vagina. Once the images were classified into either “Contracted” or “Open”, we continued down the flow diagram answering yes/no questions until arriving at the appropriate stage classification.