So a question arose in class about the vas defrens, which led me on a hunt that resulted in the following:
Human embryos are endowed with two sets of ducts: the Wolffian which typically develop into male reproductive tracts if the embryo has a Y chromosome and the Mullerian ducts, which typically develop into female reproductive tracts if it does not have a Y chromosome. (<– it’s more complicated than that.)
Whichever set of ducts don\’t develop are actively suppressed, hormonally, so they shrivel into nearly nothing.
The male reproductive tract includes the vas defrens and seminal vesicles. The latters’ job is the production of some of the fluid that sperm travels in (the rest produced by? yes, the prostate).
Non-crucial but interesting: The area of the vas defrens that meets the ducts of the seminal vesicle and the prostate is where sperm mixes with ejaculatory fluid and thus creates semen as we know it . The whole system is paired from epididymis (adjacent to the testicle) to seminal vesicle, UNTIL the prostatic region of the urethra. So that\’s important, if that sort of thing is important to you.
So much for the Wolffian ducts in males.
Now, male bodies have remnant homologues of the Mullerian ducts, such as the uterus masculinus (aka prostatic utricle), a fragment of the reproductive tract whose only notable quality is a slight tendency to get infected. The homologues aren’t large, nor are they importantly functional as far as I can tell. Evolution apparently suppressed the Mullerian ducts as much as necessary, and then stopped bothering.
But here’s the neato part, which I have only recently put together:
APPARENTLY there is NO female homologue for the seminal vesicles. Nothing. Not even a vestigial remnant like the uterus masculinus.
Fascinating, eh? It indicates the thoroughness of the eradication of the Wolffian ducts in the absence of testosterone during embryonic development.
Why would evolution invest so much in eliminating the Wolffian ducts? Something to do with the importance of protecting the female internal reproductive organs, maybe? I think there’s likely to be some actual REASON and it’s not just a byproduct of homology, because it’s not just that they don’t grow, it’s that the female body actively SHRINKS the Wolffian ducts
You probably need to be a pretty hard core nerd to find that fascinating, but boy do I find it FASCINATING.