[If] one says to his sons, “I will slaughter the pesach for the first among you to reach Jerusalem,” [then] as soon as the first one has put his head and the greater part of his body inside, he has acquired his portion, and he acquires his brothers' [portions] for them.  We may always be registered for it as long as there is [at least] an olive's volume for each one.  They may be registered or withdraw from it until it is slaughtered; R' Shimon says: Until the blood is thrown for it.

One who says to his slave, “Go out and slaughter the pesach-offering for me,” [if] he slaughtered a kid he may eat [of it, if] he slaugh-tered a lamb he may eat [of it]. [If] he slaughtered [both] a kid and a lamb he must eat of the first.  [If] he forgot what his master told him, what should he do? Let him slaughter a lamb and a kid and say: “If my master told me [to slaughter] a kid, let the kid be his and the lamb mine; and if my master told me [to slaughter] a lamb, let the lamb be his and the kid mine.”  [If] his master forgot what he had told him, both go forth to the place of burning. And they are exempt from participating in [the] second pesach.