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...