Poussin. You can buy them here. But they are just like small chickens. The embryo chick is really quite something else. You have forced me to post and image. This one is actually a duck embryo (Balut) a specialty in Vietnam. But you will get the idea. I'll post it as a spoiler. and another
This really unfortunate as I think this is probably a great recipe.
I'm sure it has nothing whatsoever to do with chicken embryos. That is just me being fanciful and silly (and looking at too many Google images). I was jesting.My wife cooks it not I. The only ingredients that I am aware of are the chicken and the noodles. The "sauce" is put together from a paste couriered to my wife by her mother in Chiand Rai.
Blimey! There could be lots of embryos hidden in that package...