Can you answer what seems like a contrediction in the rambam. If you look in sefer mitvos to see who this mitzva is on it says on the father, If you look in sefer ahava halacha 2 you will see that he says that "if no one does mila on him he must see to it himself if not he was over a positve commandment". Showing that in fact this mitva could be on the son as well. If so why did he not mention this in his sefer hamitzvot
dani, ny
The Gemara learns that the Mitzvah is on the father while the child is a juvenile (that is until he becomes Bar Mitzvah). After this the child himself becomes obligated in the Mitzvah. The Rambam in Pirush ha'Mishnah (Shabbos end of Rebbi Eliezer d'Milah) says that when the child becomes obligated the father is no longer obligated. (See Minchas Chinuch on Mitzvas Milah who discusses this point.)
The Rambam in Sefer ha'Mitzvos may not mean to say that the Mitzvah is on the father, rather that the Mitzvah is on male Jews. He refers to the Nimol as a "son" ("Ben") because the Mitzvah starts at the time when the person is a child and is normally carried out at this time.
Dov Freedman