I was watching a Crash Course on Biology YouTube video by Hank Green: Great Glands - Your Endocrine System. Hank humorously describes a sex determination experiment by Alfred Jost as follows (beginning at time 9.17 in the video):

So, he, ah, very carefully... very, very carefully (and this is a little disturbing) removed bunny embryos from their mother, and then, also very carefully, removed the part that would become the ovaries or the testes from the bunny embryos. And then, also very carefully, he put the embryos back in the momma rabbit.

What Jost found, after the bunnies were born, was that the ones that he performed the surgery on turned out to be girls. So, in the absence of gonads, and therefore hormones that specifically instructed the development of testes and the growth of a pee-pee and a deep bunny voice, he discovered that the default setting for mammalian embryos is "make it female".

Q: How did Alfred Jost actually perform this experiment?

Essentially I'm after a less superficial description of how Jost implemented this experiment in practice.

I did a bit of Googling; what I found was consistent with Hank's description, but still omits a description of how Jost excised rabbit embryo gonads (instead just asserting that he did it).

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    $\begingroup$ I assume the procedure is very similar to castration or spaying practiced on fully developed animals, but done very carefully. The harder part of the operation would be removing the embryo and putting it back without damaging it too much to keep growing. $\endgroup$
    – user137
    Aug 22, 2014 at 18:17

1 Answer 1


Check out Fig. 7 in the document at http://ipubli-inserm.inist.fr/bitstream/handle/10608/4343/MS_1991_3_263.pdf . The caption says: "Castration of a 23 day fetus. [Mother's] womb is open, the rear end of the fetus is pulled out, a flank incision is performed, and the testicle, located on the mesonephros, is exposed, then cut. After bilateral testicular removal, the fetus is re-placed in the womb. [..] For ease of explanation, an older fetus is in fact shown."

Figure 7 from the linked document

  • $\begingroup$ I don't read French, so I might be missing it, but I can't find any photographs, just some diagrams of the reproductive organs. $\endgroup$
    – user137
    Aug 22, 2014 at 21:15
  • $\begingroup$ sorry, link fixed now $\endgroup$
    – nvja
    Aug 22, 2014 at 21:27
  • $\begingroup$ That looks a lot more complicated than when I used to castrate pigs. Thanks for clarifying that. $\endgroup$
    – user137
    Aug 22, 2014 at 21:30
  • $\begingroup$ The picture I indicated shows only the castration of the embryo. Mother's oophorectomy is not described in the above link, and must be trivial. For completion, here's a rat oophorectomy: nature.com/protocolexchange/protocols/2152 $\endgroup$
    – nvja
    Aug 22, 2014 at 22:56

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