Why are some bodily fluids missing from the "Thirty Two Parts of the Body" teaching? "There are in this body head-hairs, body-hairs, nails, teeth, skin, flesh, sinews, bones, marrow, kidneys, heart, liver, pleura, spleen, lungs, intestines, intestinal tract, stomach, feces, bile, phlegm, pus, blood, sweat, fat, tears, grease, saliva, nasal mucus, synovium (oil lubricating the joints), urine, and brain in the skull." source

This seems like a pretty comprehensive list, but semen and menses are noticeably missing; although if they were included, there would obviously have to be separate male and female versions of this contemplation. 

Do we know why they are missing? Are other body parts missing? It seems unusual given how direct the Buddha's teachings normally are; so I imagine there is a reason. Thank you!
You could probably contemplate on it as blood. Women entered the Sangha somewhat later. So I would presume this meditation was taught to monks before that happened. You might have also noticed that seminal fluid is missing from the list.
Women having to contemplate on that might actually arouse their lust. Maybe it's the same case with men having to contemplate on women's period.